It's shown that there is schooling in their world, my guess is that they only get about a year off (provided they're accepted for a trainers license) to take part in the league. some who do exceptionally well for themselves might drop out to pursue careers as professional trainers. some amongst these would end up going nowhere with their lives, sadly. as for pursuing a career having retired from training, well, in a world where people have developed the kind of reliance on Pokemon as we have on electricity, being a high class trainer probably looks pretty good on a resume.