I honestly don't buy that, that choice always felt more like Tynion regressing the character to fit his story taste because he was still supposed to be going off to college in that run. Regardless, Tim is still too old to be Robin especially when looking at all his development, he should've left the role a long time ago (and he did for a bit until they regressed him) but some people at DC and certain fans don't want to let him grow up because they're too stuck on the "good ol' days" when Tim was Robin. I don't care much for Tim Drake but I do recognize that it's more detrimental to the character if they keep trying to pretend it's still the 90s and that the role of Robin still fits him; it does the character and his development a disservice.
As for Conner, he's grown ass man with a wife and kids but hey I bet some writer at DC is gonna say he's like 17 because that's how old Superboy "should" be.