What the fcuk has age got to do with it? Speed as a 34 year old centre midfielder could be used as the same argument for that matter.
wingers run up and down the wing alot,
central midfielders tend to stay in the centre of the midfield
Gary Speed has spent his career playing in the centre of the midfield, not running up and down wings
as people get older, they tend not to be able to run around as much
Gary Speed is exceptionally athletic, but running up and down the wing alot is probably asking a lot of him
and why would you turn him into a winger at this point in his career, having spent several years playing cental midfield