Remember not every who is disabled looks it. For instance: Cystic Fibrosis. Many with CF just look thin, but may have less than 30% of expected lung capacity.

That said, I have a family member who is a 16 year old soccer star who has a handicap tag. Her grandfather, who is a disabled vet, bought her car, and apparently due to how the registration works she also got the same tag. (I have no idea if she abuses this however; she seems pretty honest)