Many lovely people have been posting about their Dragon Age OCs' backgrounds! I've been thinking about this a lot for fic purposes, so here we go (and please do let me know if anything clashes with canon, still getting my bearings here!):
Inquisitor Zephyr Lavellan: I thiiiiiiink she spends her young adulthood as Second of her clan in the Free Marches mostly by default (there were very few mages born to her clan for some time that weren't quickly killed in some clash or other, and they'd been about to start negotiating with other clans to bring a mage in to support their very green 20-year-old Keeper when Zephyr finally started showing signs). Makes up for her slow start in magic with a rush of natural aptitude, emphasis on the "natural" - the more time she spends in nature, the more her magic starts to manifest, and the more comfortable she feels with it. As a very quiet, shy teenager, she's terrified at the prospect of being thrown into something of a leadership position at a young age, but the presence of her First (Deshanna Istimaethoriel, a very wry distant relative) eventually soothes her into a sense of security. She happily takes the opportunity to spend longer and longer periods of time hiking in the woods alone, ostensibly to protect her clan (which she does do, up to and including killing people she thinks would be a threat), but also because she's more content being on her own.
Her parents died shortly after she was born in a fairly pointless skirmish with humans, but her clan stepped up. She sees her First, Deshanna, and Deshanna's husband Zathel as a combo of parents/older siblings, but she was a very easy kid on the whole and stayed out of trouble, then grew up fast and extremely independent. Deshanna and Zathel have a daughter, Dira, when Zephyr is 10 years old, and she happily takes to the older-sibling role. As she gets older, she starts coming back every few months to spoil Dira with stories and handmade trinkets (she has June's vallaslin and love of creating beautiful and useful things with one's hands) from her rare visits to towns and settlements.
She's happy as long as she can escape to the woods by herself and pretend there's no larger world out there beyond what's needed for supplies on the road. She's certainly only happy when she's not being pushed into a major position of authority. So when she's only 23 years old and her Keeper tags her to go do a little spywork at the Divine Conclave, her life rapidly becomes her worst nightmare.
During the events of Inquisition, Zephyr manages to save most of her clan, but Deshanna is killed in yet another pointless skirmish after they think everything is resolved. They do find a new First from another clan to take her place (while Zephyr mostly stays on good terms with her clan, they never quite trust her the way they once did), and Zathel picks up some of the non-magical responsibilities of the Keeper along the way.
Post-Trespasser, Zephyr takes Varric up on his offer and moves to Kirkwall, where she has all kinds of wacky adventures, but about a year in, Zathel is really struggling with Dira and Zephyr surprises everyone involved (including herself) by offering to take Dira in. She winds up raising this teenager while still in her twenties herself, more or less successfully, and stays close with her, reconnecting with her Dalish roots along the way.
Zinnia "Rook" Aldwir: Zinnia grew up in a town not far from Denerim that I'm still fleshing out, to parents who were about sixteen when she was born. They weren't ready for her, their extended families disapproved for a host of reasons, and they wound up deeply resenting each other and separated when she was about four years old. Zinnia spent a lot of time being shopped around extended family in the town, and outwardly seemed like a very happy and gregarious kid, but she was beyond desperate for parental approval and deduced from a young age that she had made their lives more difficult and therefore must be what made them hate each other. Her parents were kids themselves and to some degree tried to pretend she wasn't theirs. Her dad, in an uncharacteristic burst of paternal feeling, had named her after his favorite flower, and she obsessively started cataloging plants when she was very little in a misguided attempt to win him over.
The Fifth Blight hit when she was about nine years old, and that put a lot of strain on her family (many of her family members, and I think her mother, were templars or involved in the Order in one way or another). She was taught bladework very young as some of her extended family descended into paranoia regarding mages and magic, and she took to it extremely well. Her parents were never abusive in an obvious, outward sense, but they were extremely emotionally abusive in terms of just being deeply neglectful. Zinnia compensated by being aggressively cheerful, friendly, and pleasant to be around, because it was something she could control and if she just got the words right surely people would care more about her. Every scrap her parents gave her meant everything to her, and I think she took some of her bloody-minded optimism from both parents occasionally having very awkward I Guess This Is Parenting talks about sharing and being kind and doing good in the Maker's name, and my gosh, she took that to heart.
She left around the age of 18 to study botany and, the way teens do, devised a test of her parents' affection: she'd go, and she wouldn't write to them, and she'd see if they wrote back. They didn't. She caved and wrote them a year in, and got a letter back from an aunt explaining that her parents had started dating again now that she was gone, and that she thought they could make it work this time.
Bits and pieces filtered through, mostly from extended family and friends: by the time Zinnia was 20, they'd remarried and had another child, and by all accounts were wildly happy without her. She wasn't invited to the wedding. When Zinnia was 21, the Breach in the sky opened and she watched from the sidelines, hearing rumors that many in her town had been recruited to the Red Templars. She didn't bother to find out who had followed Corypheus, or what had happened to them afterwards. She was angry for years, and then she was tired, and then she was done with it all and tumbling into adulthood alone and choosing, every day, to make that leap with optimism that tomorrow would be better.
A letter out of nowhere from an uncle confirmed that her parents had another kid, and said letter arrived when Zinnia was 25 and starting to wonder whether she was actually suited to an academic career. She started spending less time writing monographs on plant life and started spending more time training with a blade. A third kid came along when Zinnia was 27. She realized, around that time, that she hadn't actually interacted with her parents in almost a decade, and decided to close that volume of her life entirely.
She got restless. She hopped from job to job, affable and friendly and always making surface-level connections, including the odd romantic one. When she was about 30, she joined the Veil Jumpers mostly out of an appreciation for the adrenaline-fueled companionship that emerged from it, and she met Varric and Harding, and things started to change in the year she traveled with them. She let herself build deeper relationships for the first time in a long time. And when a new blight started spreading across the South, and the Inquisitor reached out with news of her family, kept safe and sound along with Harding's, Zinnia wondered what might have been, and hated herself for wondering.