Humans have had about 10,000 years of interesting & productive history. At best, a human lifespan is about 100 years. That's one hundred 100-year lives back-to-back. That's...not much at all.
An average generation was probably about 40 years for most of that. So I'd say about 200-300 generations. It's not much, but I still kind of feel that as a species we haven't done very much at all in that time. Personally I prefer to think we're in our teenage years as a species.