Is it worth to make a season char now or wait till next season? Im a casual player, just returned and want to make a new character.

It depends on how fast you are, if you got all day time to play on seasons and can level it fast then i'd say yes

Since you said you're a casual returning player im gonna assume that's not the case, since the season will end on Sept 28. You probably won't be able to complete the full season then. However you still might get some rewards out of it.

Personally I'd advice you to wait on the next season :)

Season lasts until the end of the month.
Even if you have to do all the quests (aka can't do the simplified questline) it takes roughly a week to be done and full PEN.
So yeah, you can still make it on time if you start now. ;)