I think most people assume all the apostles would have been about the same age as Jesus (30-33), with the exception of John. Most traditions, as well as a lot of artwork, usually portray him as a teenager. It is also assumed he was the youngest because of the dating of the Book of Revelation, which it is thought that he authored.
I do not have any Biblical references to support this. Actually, I don't think there really is anything in the Bible which clearly states how old the apostles were. There are a few verses which give us some rather vague clues with regard to some of the apostles' surviving relatives. For example, Matthew 8:14 states that Peter still had a living mother-in-law. Matthew 27:56 says that "the mother of Zebedee's children (James and John)" was at the foot of the cross. However, since most women married quite young in those days, this really doesn't help much with trying to guess the age of the apostles.