Possible Clues:

• Little League rule
• Take note: legitimate manoeuvring is what bars under-18s from voting
• 19, for N.B.A. players
• I am legit (anag)
• What some amusement park rides have
• 25, for the draft
• Provision for holding certain jobs
• Colourless Arthurian site setter's object too old, I might say
• Regulation based on year of birth that sets down when one can no longer do something
• It can mean one is too young or too old