Don't need the 28th. It should already exist in the "equal protection" clause of the 14th. On the other hand, the 14th probably needs to be repealed as well.
Plus we still need that term limit ammendment for Congress as well as the Supreme Court:
- House limited to 3 terms of 2 years each,
- Senate limited to 2 terms of 6 years each,
- Supreme Court limited to 25 years or age 75, whichever comes first.