Rooney turns 25 tomorrow, so I doubt he is past his prime.
I don't think he has regained full fitness following last season's injuries. And being at the World Cup this summer meant he returned this season at less than 100%. And his head hasn't been fully focused on football, distracted by his problems with prostitutes.
I'm sure then new ?250k per week (as reported in the Daily Mirror, today) contract should help him find his form.
Annoyingly today Fulham returned to their bad habit of a few seasons ago - taking a 1-0 lead, but losing 2-1.