If a star tortoise is 4 inches how old is it approximately? What about 5 inches? I am looking to buy one and it has to be at least 4 inches and I am a little curious how old of a tortoise I would be buying.. Thanks for any help given.

Hard to say, but possibly 4 yoa, maybe older, depends on how well/what it's been fed.

Tortoise age is almost impossible to guess accurately. They grow at different rates depending on what they eat.