A 23 year old in the 17th century would expect to live nearly as long as a 23 year old today- the depressed life expectancy statistics are largely due to the fact that 3 out of 4 children died before they hit the age of five.
http://www.infoplease.com/ipa/A0005140.html
So the average 20 year old in 1850 could expect to live an additional 40 years, to roughly age 60. The curve started flattening after WW1 and continued doing so until around the 70s and 80s.
Here's hoping for the hockey stick.
I suspect there were significant differences in life expectancy between the 17th century and 1850.