Tooker [#4]
They've had issues in the past with curfew and work hours limits for under 18 talent.
Most under 18 also have obligations with school that will severely hamper their ability to travel to another state/country and play matches. Much easier to just have them play T2 from their bedrooms until they finish schooling .
I feel like it just kills off young talent so much and especially just makes people who win ascension less rewarding (bleed)
Just to add, the point of ascension from an org pov is almost strictly about qualifying. Riot is almost certainly going to expand partnership slots, so orgs want to interact with Riot as much as possible so they get selected. That's my guess as to why you'll see a lot of ascension teams field rosters with under 18 talent or more than one import (à la JDG). Even if they know their roster will be worse after they qualify, they still want to get that 2-year contract.