Yes, it's possible to "own your own" 529 account. You could open a 529 account today and name yourself as the beneficiary, or change the beneficiary on an account you own from someone else to yourself.
When the account owner/beneficiary of a custodial 529 reaches the age of majority, the account owner and former minor simply takes control of the account; the custodian steps aside. There is no need to transfer the account, cash it out or pay any taxes and penalties.
Opening a standard UTMA account and then converting the funds in that account to a 529 when the minor gets close to college age is a problematic strategy. A 529 account can only be funded with cash, so you would have to liquidate the UTMA account and pay any taxes owed on the gains in order to fund a 529. This defeats much of the purpose of having a 529 account in the first place: long-term tax free growth and use of the money, if used for qualified education expenses.