I don't think there's any way around the age limit for UTMA accounts. You would probably need to have established an alternate vehicle (such as a trust) if you wanted to set up a different schedule for transferring assets.
Sounds like the money, legally speaking, belongs to your kid now. Of course there's nothing stopping you from implying that use of those funds for a non-approved purpose could have future consequences (less help with school, less inheritance, etc.). I'll leave it to you to decide whether that will be necessary or appropriate in your situation.