I don't think that's literally true. The average newborn baby might have been unlikely to make it to 30. That's because many didn't make it past their first few years. If you average in the childhood deaths, the mean life expectancy for everyone comes down.
If somebody lived long enough to be a worker, and wasn't a worker in an extremely dangerous profession like mining or the military, he or she probably lived well beyond 30. Many Romans lived into what we would consider old age. (In ancient literature, 80 was considered a full life.) Romans' hair didn't turn white at 20 or anything like that.
Certainly the age-demographics of the Roman population were different than our own. There were more infants in their world, since most women of child bearing age spent much of their time pregnant. But many of the infants died in their early years so the big bulge in number of babies soon fell. And the number of elderly retirement-age people in their 70's and older was a lot lower than we see in our own populations, since many diseases and injuries that are treatable now killed people off.
I don't think that the blessings of God had anything to do with the lengthening of the average lifespan. More relevant is the contribution of medical science to reducing childhood and subsequent mortality. Of course that development, which most of us would consider a good thing, has led to an explosion of the human population on this planet with its own problems.