Running in speed with an older horse?

If the horse has already been trained for speed. Then I don't see a problem with it. My friend's horse is 24 and other than trail riding, all she does is speed and barrels, and at the most recent Horse Show, they were placing 1st and 2nd in all of their speed classes! I was totally shocked when I found out her mare was 24, she always acts so much younger than that! Buut I would get a vet to check out the horse first, just incase, ya never know!