His convict record (URL at reply #20) can be edited by anyone who is registered (free) or has a Google or Facebook account. 
I think the person who edited his DoB has assumed that William was the son of William Ward and Anne Catherine Hennell baptised at the Old Jewry Church in 1799, an has ignored the age stated in his death certificate and newspaper notices.
Regarding the Old Bailey record, could he have said he didn't know his age because he was an orphan and his age was assumed?  
I understand that a 17 year old boy and a 24 year old man would have looked different, but I also think that a 76 year old man wouldn't have looked like a 83 year old man. Maybe the truth is somewhere in between these ages?
I'm also interested in the 'nearly 50'  supposed mother, what was her name?