There has never been a period where most humans would die at ~30.

While life expectancy at birth was ~30 for the whole history of humanity up until the mid 20th century, this doesn't in any way mean that average people died in their 30s. Instead, life expectancy was highly bi-modal: most people died as children (most before age 1, but still a large number before age ~15), and most of those that didn't die as children lived into their mid to late 50s.