Whilst there is dispute about the age of the big bloke, a very cogent argument for an early age is given in the only book I know of which is entirely devoted to the subject – The Cerne Giant by Rodney Castleden.
Although he’s a big lad, he hasn’t always been quite so well endowed, there is an early edwardian photographic postcard which clearly shows him having a navel. This was incorporated into his penis when the giant was re-cut in 1908.