Yoda lost because of old age? Somewhat true. But no. Sidious was smarter, and used the field to his advantage. And no way in HELL does Ataru defy age. It utilizies the most flips, spins, and physically impossible acrobatics of all the forms. I don't know what your talking about.
Anakin would defeat Grievous. Obi-Wan took time because he was conservative; a Soresu Master. Anakin is a Master of Djem So, an aggressive form, so he would press the attack against Grievous and eventually win. Not easily, but he will. Doesn't have experience? He fought and killed Assaj Ventress, dueled Dooku twice and killed him the second time, became a Jedi Knight without going through the trials, etc. He had a LOT of experience. And, oh, Anakin killed those great Jedi Masters. With so much foresight.
Mace would have improved greatly as well as Dooku, after practicing and perfecting his fighting style and learning about the Force. Dooku learned more force-wise, but even if he did take Mace, it would be an impossibly hard battle. In Dark Rendezvous, Yoda stated that out of all the other Jedi, Mace was Dooku's only equal, meaning the battle could go either way.