so, okay, first of all, it’s worth noting that Baron is, like, a worse version of Snape. which, ironically, is close to the shallow perceptions of Snape.
whatever the nature of his love for Lily, one way or another it was never obsession, and he would never have killed her intentionally.
moving on. the BB, most likely, has, like, a, i’d say, Black temperament. [like, it’s not that it would affect Snape in any way, because, well, his issues with one single Black wouldn’t have influenced that at all. and yeah, i think it’s a common thing among nobles and purebloods] but i'm mentioning it simply because he doesn’t have a Snape-ish temperament. not at all.
then… Severus would have known him primarily as the slytherin ghost from the age of 11.
we genuinely know absolutely nothing about his relationship with Severus, but we do know that the Baron.was very proud of Slytherin’s successes, and considering that… Snape secured the quidditch victory six years running. i’d guess their relationship was at the very least quite decent.
then, let’s say, we don’t know whether Snape knew the whole story about Helena, because the house ghosts themselves didn’t know about it. [or they knew but absolutely didn’t talk about it] on the other hand, i like to headcanon that after Lily’s death… Severus, most likely ~ just like Harry after Sirius's death ~ tried to find out something about the world beyond, so to speak, from first-hand accounts. and most logically, given his position at the school and his status as a Slytherin, it would have been logical to ask the BB about it. <that’s a completely insignificant headcanon, but in my mind, yeah, he knows that story>
Helena ran away from school while still a student. meanwhile, Rowena Ravenclaw, after falling ill [mortally ill], asked the Bloody Baron to find Helena because he was in love with her, at what point this happened is hard to say.
on the one hand, one can really speculate that if she was able to ask the Baron because she was at the school as a teacher and he was STILL at school, then that would mean the Baron is practically a child, [under 18. or 18].
but on the other hand > she could simply send him an owl because she remembered that this boy was genuinely obsessed with her daughter ……then i’d say that could be any age up to 30, and most likely rather young. the closer to 18 > the more probable.
/well, after 30 is also possible, but it’s just very unlikely, [which absolutely doesn’t match his appearance in the film. are we even surprised at this point??]
unlikely because.... well, imagine: you’re a teacher whose daughter ran away, ran away around, like, 17, let’s say, or earlier. and you remembered that there was once some lad who fancied your daughter, and now he’s somewhere around 40 [so it was more than 20 years ago] and you write to him to get him to find your daughter. … well, that’s, like, you know, quite an unlikely scenario, so i’m inclined to think he was quite young. forever young. lul.