I wouldn't say I completely "grew out" of anime, but I have a lot less patience for it. Gone are the days when I could watch anime for days on end, even mediocre stuff and still enjoy it. Nowadays I can watch 2-3 episodes of a good anime, and then my desire to watch is gone for a few days until I "recharge". And I agree with finding most of the protagonists just unlikable or unrelatable.
There IS anime out there for adults though, they're not all teens, and that feels good. I found a little gem recently called Hakumei and Mikochi about two little gnome women who like... live their lives and make soap to sell at the local market and sample wine with their friend the pub owner (the story handles their relationship in the old-fashioned "we never say the "L" word but everyone around them treats them like a married couple" way). There's no grandiose plot and no high stakes but the whole thing feels like a good cup of hot chocolate. ETA: Or, how could I forget Shirobako, about five 20-something women building their careers in the animation industry?