In Bundesliga there are maybe 2-3 top clubs (Bayern München, Schalke, Hamburg). Hoffenheim was a sensation when they emerged, a tiny club that started to win against the giants. Now, the magic is gone and I don't think they will be as good as they were. I think Vedad has ambition and would want to play in PL, La Liga or Serie A but at the form that he is in right now I don't know what "big" club would want to buy him.
There are some offers from PL from smaller clubs, but Im afraid that is he moves to England and does not perform well he will be stuck in a crappy team and just rotten away. I would prefer to see him play one or two more seasons in a bigger more well known german club where he can get in form again and then when he starts playing like in the old days move abroad.
But you are right, he is young and there is time. However, his transfer will be affected by the owner of Hoffenheim. The owner is a billionair and even if a club would make an offer to buy Vedo (no matter how high) he can turn it down because he is not interested or dependent on money as many other clubs are.
There are some papers that have written that the HH coach is pretty upset with Vedad and that Vedo has "used up his last chance" with the coach. I think this might affect his performance and loyalty to the club.