Rooney was fantastic at 18, but in my opinion a 18 year old Rooney was better than a 25 year old Rooney and a 25 year old Rooney was better than a 32 year old Rooney.
Whilst Rooney was world class at 25, i still don't think he's career developed how it should have, he just never looked after himself, i called it back in 2009 when he was around 25 that he had a short-battery life and got a lot shit for it, i compared him to Adriano, a boy-wonder (like Rooney) tipped to be the next L. Ronaldo, career never went that way though (like Rooney) and batteries expired around 27 (like Rooney).
Sure Rooney is leading scorer of Manchester United and England, but think that's slightly embarrassing to be honest with you, as i wouldn't consider him to be a 'true' legend of the game.
As for the Kane comparisons, as someone else pointed out totally different players. Kane is more comparable to prime Shearer (Blackburn years/early Newcastle) but even those 2 were different players.