Higuain is not built like Ronaldo. I don't think Higuain's age are helping the cause, imo he will just get slower with the age and play more with the back forced to the goal. He's the type of striker who would probably work only in Italy when he reaches 31-34.
On the one hand I think a lot of strikers do well to be a bit on the heavier side. It makes it easier for them to shield the ball from defenders. So far I don't think Piggy is suffering from the extra weight.
On the other hand you just have to take a quick look at Piggy's pictures from a couple of years ago and you can see that his metabolism isn't really changing in the right direction. If things get even worse, we're going to have a very very fat man in two years.
