His hair points to a time jump; his face does not, and The Walking Dead isn’t exactly a show that doesn’t know how to use makeup to change actors’ appearances.
That said, there are reasons why the time jump theory doesn’t make total sense.
For one thing, Andrew Lincoln looks like a middle-aged man wearing a grey beard and grey wig.
Sure, it would be convenient if we got to skip most of Maggie’s pregnancy, but aging up the entire cast for a time jump might not be practical for the show.