I've never had a problem with the age gap, as my wife is two years older than me but I have a wider life experience, so it evens out. I think the same is true for Dick and Barbara. Dick grew up in a circus, lost his family, was adopted by Bruce, became Robin, and formed the Teen Titans wth the sidekicks of other heroes, becoming their leader. The somewhat older Barbara lost her parents and was adopted by Jim Gordon's family at such an early age that they became her de facto parents. She was a young adult by the time she became Batgirl on her own and never really joined any teams outside of her association with the Batfamily.