Actually, funny thing, I've always felt the reverse, that his life is so fast paced and frenetic that he doesn't realize how much time has passed. I've frequently said Nine could've lived for 100s of years before meeting Rose and just never slowed down long enough to see his reflection until he meets her. I just can't imagine anyone travelling through time frnetically and constantly bouncing from one adventure to the next for years (or centuries) and having any clue how much time has passed. As you say, Amy and Rory don't feel like 10 years has passed, but they know it has from their friends commenting on their aging.
One Day I hope to be the Man my Cat thinks I am
Where are we going? And why are we in this Handbasket?