75 years of nation-wide life expectancy is also likely to include early deaths due to accidents, cancer and such. People who die of "old age" typically do later than 75.
When people talks about life expectancy 99.99% of the time they mean life expectancy at birth, at every year the life expectancy change. Using this life table someone with 61 years, have a life expectancy of 19.7 years, that means he's expected to live until he's 80.
Yep, and that was true even going all the way back through history. People weren't routinely dying in their 30s or whatever before modern medicine; it's just that a lot more of them were dying in infancy/early childhood and that brought down the average. (That's the situation anti-vaxxers are trying to go back to, BTW.)