By that I meant, consider the level of your trainer. If they've competed in Gyms and been a trainer a while then lv. 40 would make sense, whereas if they've only started recently then 10-20 might be more reasonable.
And, of course, you can always have a range of levels :3 I think I will state a cap of lv. 40 for now though, just to add some kind of boundary.
(Did I even answer your question? Idk XD)