Yeah, a bit bored too. But I guess it's because each and every GT feels like a better version of its predecessor. How many GT's can you play? How many... Halo's? God of War's? It's not that it's a bad game per se, just that we've replayed the likes of it again and again, even in its own series. It's easy to "burn" playing the same kind of game.
The solution is simple: put it aside and play X-Com, Civ or something. Play some FPSs, and DON'T play "other games with cars" for not days or weeks, but months. Then, in 3-4 months, come back to it. You'll love it again. For a while. Then get bored. Again.
That comes from a 37 year old gamer who's gotten bored of pretty much everything. Again. And again. And learn how to live with it and love it.
![Smile :) :)](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)