what do YOU want?
If you are fine with the amount of time your are spending with your gf, why let you buddies pull this shit attitude with you?
It seems like you are spending both 'couple' time and time conducive to your well-being...it just happens to be with the same person. You appear to be happy, content, and enjoying this time and your friends may be jealous. It is not like you are not inviting them to join.
On the flip side, just make sure you are happy with the situation....it never hurts to spend a day or so a week have a little bit of 'you' time.
And, you are kind of right about the age thing...it seems to me (and a lot of others), that as we get older, we tend to spend more time with our SO instead of our friends....its not a bad thing, it just happens.
If you are happy, keep doing what you are doing. Your friends may be a bit jealous as you seem to have a constructive healthy relationship....they may not be at that point in their life yet. They will get use to it.
Also, way to go on having an active life with a great partner
