Billy is about as old as he appears to be, being in his early-to-mid 20s. As an android, he's always had the maturity of an adult, though. He's actually one of the oldest out of the Cunning Hares, even if he doesn't seem so at first glance. Speaking of Gentle House, they're like family to him. He frequently acts as an older brother even if, also frequently, he isn't respected as such.
He was built as a combat weapon manufactured for war, so he didn't need to learn tactical bullet arts or how to drive. Despite being a durable war machine, his body is slightly aged due to him being a product of lost technology. He isn't outmoded, per say, but doesn't perform as well as he did a decade ago. All of the repairs to his body are by his own hand, and he’s documented most of it within a notebook because he didn't come with an instruction manual.
His body has doll-esc joints and articulation, including ball joints, and it has been modified so he's able to experience things closer to how humans do, like temperature sensitivity and a pain threshold. Also, his hair is synthetic, so it's very soft.
Most robots of his generation don't need to sleep, only recharge, but he does anyway. He's even learnt how to dream.
Billy always smells ever so faintly of machine oil because it's required to keep his body operational. He masks it with various scents, one of his favourites being vanilla.
It's likely that he wasn't always as autonomous as he is currently, and only began to change once he started his own journey, becoming his own person. Mirroring the real Billy the Kid, he was ‘orphaned’ from his former home when he was (technically) 15. Billy values freedom greatly, but still follows Nicole unquestioningly because he was built to follow orders and feels most comfortable working under somebody. She’s usually the highest form of authority that comes to his mind, and programming-wise he recognises her as his ‘Boss’.
"Even if I agree, the Starlight Knights wouldn’t agree!"
"...And even if the Starlight Knights agreed, Nicole wouldn’t agree!"
He's probably a hoplophiliac.
Ironically for a gunslinger, Billy’s eyesight isn’t the best. He often has to squint and/or close one eye to get a clearer picture, making him slightly nearsighted and with possible diplopia in human terms. His model type was built for its accuracy, which is a double-edged sword. He’s still incredibly efficient without perfect vision, making use of his enhanced movement sensors- but his degraded vision is very difficult to fix without the proper materials. This is why it has gone unrepaired.
He has a resting bitch face. His default expression is often mistaken for an angry one, but it’s literally just his face.
i do deeply enjoy having normal friends because they'll say shit like "surely nobody finds [random robot character] fuckable right" and i get to be like buddy. my mutuals are doing insane things to his digital cervix