actually, i think park ranger is exactly the right sort of thing for him to be doing, and here’s why:
we see that even after they’re let loose onto the world, none of the trio actually directly initiate conflict. the closest they came to that was stealing the van, and even then they mostly ignored the drivers at the rest stop. from there, every instance of fighting they got into where harm came to people was due to an odd sense of “self defense” if you will. the biker gang that chased them down had the intent to harm them first, and they reacted accordingly. the police officers who tried to arrest them only had their car blown up, and the officers who chased them weren’t killed, just incredibly startled when 18 split their car in half. even during 18’s fight with Vegeta, our dear Prince of All (3) Saiyans did far more damage than 18 did, and 17 only stepped in after the z senshi got involved, and even that was after an incredibly clear and fair warning.
what this has always told me when i noticed the pattern was that neither of the twins are particularly violent by nature, even after being brainwashed and tortured by Gero to be exactly that. they’re teenagers who’ve just come out of incredible trauma, and are trying to figure out what to do with themselves now that they don’t feel like they have a past to return to, or a future to chase.
so given those circumstances, a lot of the decisions they made were incredibly on-the-spot. everything they did once they escaped was for and in the moment, and that sort of thinking is exactly the kind of reflexive personality that is well suited to jobs that require being more hands on and confrontational. after 17 was beaten by cell, his already fragile and terrified sense of self was effectively completely broken. he had nothing to front for anymore, and i think in a lot of ways, it mellowed him out (as desperately sad as the method was ;m;). so now he still has that split-second wit to deal with, but none of the ego, and i’d like to think that 17 eventually settled into whatever mountain town he got the job in while looking for his sister. as it happened, he got the job, (and apparently a wife and munchkins but that’s a squeally elated ramble for later) and it seemed to bring some of that confidence back. while i will never ever accept GT as canon, and buu saga is pretty dubious, i will say that toriyama’s latest Q&A was not the first time we’ve heard of 17’s career choice, as there is a scene where we see him holding two men (presumably poachers) at gunpoint. so it’s not like this was something that happened on the fly because a question was asked about it.
anyway, long answer to basically say i think being able to enjoy his life for once gives him a lot of room for growth and personal adventure, which is perfectly in line with ranger work, besides being hilariously ironic that he is effectively a police officer now. as for pizza delivery and mechanics, i think if he were to take on a job that so intrinsically required being pleasant with other people on the regular, he’d need to learn how to communicate without being a total brat first.