Why didn't Madara start his own plan when he was still young?
Madara didn't know he was going to awaken the Rinnegan. He knew about the story with the Sage of Six Paths and the Juubi, he also probably knew about the existence of the Eternal Tsukuyomi. But without the Rinnegan, his plan couldn't have succeeded at all (because the Rinnegan is needed for the Gedo Mazo).

Since Madara didn't know he was going to awaken the Rinnegan, or what the requirements were, he couldn't have started his plan.

Sure, in retrospect, if he had known he would awaken the Rinnegan at a later point, starting to collect the Bijuu early might have been a clever move.



Note that even his current plan had flaws in it:


Obito never planned to resurrect Madara. It was Kabuto who made the fatal mistake of reanimating him (having been tempted by Black Zetsu with Madara's corpse), and thinking he could control him. Obito's plan was to complete the Infinite Tsukuyomi himself, and create a world in which Rin lives.