Assume human lifespan is now 150-200 years: how differently would people treat the first 50 years of life? What does education and choosing what to learn change with that much extra life?

A lot depends on what other enhancements we get to ourselves during that same time.

I don't think we'll be able to reverse aging without learning enough about ourselves to make lots of other modifications. At the very least, imagine pulling your brain plasticity back to 4-year-old levels and learning more languages.

What does learning multiple languages have to do with brain plasticity?