Are horses over 3 years old not able to race in horse racing and has a female horse ever won the triple crown?

Yes horses over 3 years old can and do race. The Santa Anita Handicap for instance is only for 4 year olds and older. And no a filly has never won the TC as of yet. Fillies kinda have their own Triple Crown, its called the Triple Tiara, though its not as well known. It consists of the Acorn Stakes, Coaching Club American Oaks, and Alabama Stakes. Not sure about the exact order. Hopefully we will see another TC winner, and more interestingly a female TC winner!