Okay, I'm not into Jace, and I also write experianced Robb, but here me out:
Robb being a virgin makes more sense, since he grew up raised by Ned and Catelyn. He's taught to respect honour both his own and other womens, considering in the books he marries Jeyne to protect *her* honour, not his own. So, him being a virgin makes more sense because he wouldn't want to put women in that situation at that point in his life, and is fine saving his own for his future wife.
Jace, grew up with literally no boundries about relationships. His father might not be his father, because hes pretty sure his mother was actually banging the commander of the city watch but he doesnt know if his father knows or if hes supposed to know. But then his supposed father "dies" and its rumoured to be by his mother and her uncle so that they could then marry right away.
Jace did not grow up with the boundries about love and marriage and honour. He just logically is more likely to not be a virgin because he didn't have good role models growing up in regards to sexual relationships. But Robb did, so he'd be more likely to not sleep with someone before he was married or willing to marry them.
I mean, my Robb fucks don't get me wrong, but logically, I think Jace not being a virgin makes more sense considering he did not have a stable example to grow up following in regards to that sort of thing.
Robb grew up valuing honour and seeing a happy, loving marriage between his mother and father. He had the better role models to value his own virtue and other womens virtues in regards to premarital sex. Jace did not.
u summed up my thoughts so well it’s crazy. i just didn’t wanna start virgin jace discourse again 😭
robb was raised with ned & cat as example, and the starks are inherently respectful — ned’s parenting of honor aside. he seems like the type to save himself for his future wife. he was raised as heir to winterfell, he knew he’d have to marry eventually anyways, and that’s just duty. it’s not even mentioning his character and the way his parents raised him
rhaenyra has pretty much excused all of her sons actions/enforced no boundaries (aemond losing his eye example A), and that combined with his parentage discourse definitely makes me think jace would have experience. he’s a prince, he’d never be denied, and he’s never been taught anything different 🤷♀️