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?

This is so dependent on how life is actually extended. People now live much longer, but there is a period of almost 25 years at the end of long life spans that hardly can be treated as “just additional life” (93 year olds may be more numerous than ever, but they often have a very narrow range of activity options).