Would it be a good idea for the human population to have their first partner to be significantly older so they can share the experience?

Bad idea. Ive found that when a partener is much older, they *intentionally or not* cause the younger to go through personal development in a way that is too accelerated, superficial, and artificial. Later when the relationship ends (and it almost always does) the younger is left a stranger to their peers. They have to re-start the maturing process, kind of like when you speed skim a textbook. You read it, but you probably didnt absorb enough to have learned anything. The younger could be left feeling like they really missed out on their youth at having to experiance with an older person's lack of intrepidity.