Don’t know if I messed up on my other post, or if I said something really controversial 😉
About boys going out at 21: fine if he’s ready to accept all his responsibilities. But if it means another 2 years, say, of support, that’s ridiculous.
And about mentors: R’ Avraham Birnbaum in a Yated article a month or so ago mentioned the problem with boys and mentors. Considering that a good boy will likely be in 3 yeshivos by shidduchim age (US post high school, E”Y, Lakewood) there is less ease in developing an ongoing relationship.