You're not understanding my argument. Within the current way we do things, whatever age you pick is the age the transition period starts for a big fraction of people. Just picking a higher age doesn't work.
If anything, based on the median in the US right now, we should be introducing more self-determination earlier.
Not without impacting other political aspects. Remember we only lowered the voting age to 18 some 50 years ago to justify the ability to send more kids to a war we started. And that's only the tip of the iceberg.