Giving Kids Incremental Control Without Creating Separate Trust

My wife and I are looking into creating a trust for our kids that gives them incremental control over their trusts as they get older. At 28, they get 20% of the whole trust to manage and make decisions for, at 35, they get another chunk of the original trust, at 40 they get control over the whole thing. Can this be done within a single trust entity? So long as both portions are managed by the same financial instiution, can a descendant have total control over one "account" within the same trust, and the guardian trustee have control over the other portion? Are there major drawbacks to this? We live in Colorado, if that makes a difference. I'm grateful for any insights anyone has into this subject.
Thanks,
A Very PuzzledParent!