I agree with pretty much everything people have been saying here.
ANIME FOR ALL AGES!
If you're feeling that you're growing out of anime as a stage in your life, than I believe it is fine to decide to let it go--but I don't believe you should try to get out of it just because there's a misconception out there that it's just for kids (of course this can also depend about how much others' opinions matter to you.)
I know many anime lovers who are over their twenties. I believe I saw a poll a long time ago asking the ages for anime lovers; the largest seemed to be teens, but the second largest was over 18 or over twenty....
I'll be eighteen this January and I have no plans to "outgrow" anime. ^__^ Speaking as a girl, I think my interest in a guy goes up if he likes anime---I would definitely like for him to like anime even if he doesn't as much as me. I wish there were more Christian + anime combination in guys... So stand up and be a rare species!
Suggestion: like what others have said, in the situation in which a girlfriend scoffs at anime, perhaps try and see if she would understand it more. When she does, and at least accepts you for it if not becoming hooked herself, than at least this worry of yours won't be a porblem. ^_^
--star