In terms of winning a Slam - I'd give him til he retires.
Because you can just never rule him out. Sampras was winning slams in his 30's. Federer's still going strong. Other players have peaked in their late twenties (Ferrer, Fish, Bogomolov). Ljubicic won his first Masters at 31. Okay it's not a Slam. But you can't rule Andy out.
In terms of becoming the best in the world (and seriously, you can't rule that out just yet - I doubt many gave Djokovic much chance of being the best in the world just over a year ago. Now look..) then yes, two years seems reasonable.
But in this day and age, many players are peaking well into their 20's, rather than barely into them like 10-20 years ago.
It's just impossible to say. The ability is there. The consistency not. But Djokovic was the same a year ago. Consistency is something that will improve with experience. And a Grand Slam is just one tournament. You never know when someone's going to have that one tournament where they just go all the way.
Federer isn't going to be around for much longer, and I don't think Nadal will be either. Whereas I think Andy will be able to play into his 30's at a similar level as now. Sure, he may peak at 25-26, but I can see him keeping that level for a few years after and certainly not rapidly regressing once he hits 28/29. And at the moment, it doesn't look like anyone else is going to suddenly start challenging for Slams, bar maybe Del Potro.
Andy has always had Del Potro's number and has proved he can beat Djokovic in over 1/3 of their encounters. When you think of it objectively, in a couple of years time you would imagine it would be Djokovic, Andy and Del Potro fighting it out. Eventually Andy will get the better of them when it matters.
So I will just say this - believe. Tennis is no longer the young man's sport it once was, and many players are playing into their 30's. Andy has at least 7-8 years yet before he will even consider retirement. That's around 30 Slams. He may not win one when he's at his peak, but I have no doubt he'll still be contending them for any years to come. And he will win one. Eventually. Whether it's this year, whether it's in five years, I have no doubt he will win one.
Well said Madhatter,
Actually I'll go further & say I think he is primed to be the next No 1.
If he can just get a grip of himself, as it is mastery over himself now that is the issue. He's not a little boy anymore, its time for him to get a hold on his emotions. And despite the relapse into the bad old days that we witnessed in this tournament, Andy knows full well that he has to get over this stage finally grow up as a human being and move on. Life will make him do it. Its inevitable.
Dont agree that there havent been improvements either, if you abstract Monte Carlo from the equation, which was dreadful. There have been major improvements in attitude, serve, forhand court position & so on.
I am willing to see this just as a temporary blip as there were certainly reasons for it.
Players are taking longer to evolve this much is clear in the results on the tour and I have said it for ages.
Onwards and upwards.