You're really into this idea that people own their children like cars, or, you know, slaves. I've been married 5 years and I've never spoken to my in laws, and my wife would hit the ceiling if I suggested that as a grown ass woman she needed her dad's permission to do anything, including me.
What if someone asks permission and you say no? Do you think he's going to be all, "Well, sorry, honey. I need your ring back because your dad said no. He also says you have to move back into your old bedroom and it's past your bedtime."
Who asks permission when you're going to do it anyway if they say no? Especially when you'd be inclined to flip a table and tell them to go fuck themselves in that scenario.
I don't think I could say no. That would probably drive the daughter away and ruin the relationship. I think it would be more about expectations. Not just about growing up and becoming adults because a lot of people who are getting married are past the immature age and are ready for this step. I mean take the opportunity to be completely honest with each other, and it should work both ways.
When I talked to my FIL, his only concern was that we were still fairly young and his daughter really hadn't been in any other serious relationships. She didn't get to "see the world" without me. We had been together for about 3 years and were living together for about two years before we got married, we were both past the immaturity stage, had good jobs, and a nice household, a couple pets. We were ready and it's worked out great.
My brother got married a little younger than me, asked me to be his best man, our whole side of the family wanted to tell him to not get married. His girlfriend was young, selfish, immature and a hair dresser. I wouldn't do it, it was his mistake to make, I voiced my concerns one time and told him I would never bring it up again and told the rest of my family to keep their mouths shut. He had a beautiful wedding, and a horrible divorce about a year later. His wife turned 21 and wanted to go out, my brother had started a new career and was working a lot of hours. She ended up sleeping with his best friend. It got ugly, but had I told him not to marry her, it would have ruined our relationship, and what if it would have worked out? These were his lessons to learn and not mine to teach.