Jan is three and a half years late to his quarter-life crisis, technically speaking; but, for one thing, the number 80 bears essentially no relationship to his expected lifespan (in one direction if you're calculating from the best that medical science has to offer, and in the other if you're factoring in his lifestyle).
For another thing, what he lacks in timeliness, he makes up for in scale.
At twenty-two, Jan, aside from the secret vice that is Thari, is the very model of a moral Jedi Padawan. He eschews attachment and jealousy and greed and fear and anger and hate and suffering and passion and excitement and the dozen or so other emotions Jedi are encouraged to avoid indulging in. He dances through lightsaber forms with straightforward flawlessness. He communes with the Force and seeks peace before war and practices obedience and humility and secures delicate diplomatic compromises and mends his own robes.
The next year, Thari dies.
She wasn't a combatant. She wasn't even a fucking combatant. She wasn't even a Jedi -- she'd passed the initiate tests, all those years ago, and then announced that learning to wave a shiny sword around was a waste of her time and energy, and ten years later while Jan was swinging a shiny fucking sword around, she was doing half the cryptography for the Jedi Order, but no Jedi training meant no danger sense meant an untrained civilian with a blaster could walk up behind her and shoot her in the head point blank.
Attachment leads to jealousy leads to fuck it, Jan decides, if mourning his sister means the Dark Side of the Force, then he has a new life plan.
He kills his Master. He talks her into bed, he watches her betray her ideals for the sake of a quick fuck, he kisses her and he puts his hand through her ribcage beneath her breastbone and pulls it out again with her heart in it and he can taste her heart's blood foul in her mouth.
He cuts off his Padawan braid and tucks it, coiled, into her dead hand, a parody of the gift of a Padawan become Knight: well done, Master, you taught me my last lesson. I'm all grown up now.
(He'd have burned it on his sister's pyre, instead, but they burned her without him. No one ever knew he was her brother.)
Jan wears his bloodstained robes. He carries his lightsaber. (He's no Jedi, now, but they aren't the only ones who fight with shiny swords.) He kills seven men, of the age and sex and species of the assassin, leaves them naked and bleeding in their sisters' beds. It's a message, of sorts, he supposes, though who to is obscure even to him.
The Order send Knights after him, but by the time they're there, he's gone.
Jan, twenty-three, stands in bloody robes in the cramped bathroom of a hijacked transport, puts on eyeliner too thick in the tiny mirror, and wonders what there is left for him in the galaxy.
Maybe he'll burn some books.