Parent is likely a troll, but I'm going into the numbers.
From 1980 to 2008, the average investigator age at NIH has gone from 39 to 51. Source: http://www.plosone.org/article...
In 1980, I had to derive the damn number (http://www.bls.gov/opub/mlr/1982/07/rpt2full.pdf), the median worker age is approximately ~31, while the 2013 average worker age is 42.4 (http://www.bls.gov/cps/industry_age.htm).
The average age of workers has increased by 11 years while the average age of investigators has increased by 12 years.
Research grants are a "winner take all" system where the total amount of research money is roughly constant (http://cdn.americanprogress.org/wp-content/uploads/2014/03/NIHfunding-fig1.png). Essentially, the older researchers are displacing the younger ones in the field through simply outcompeting for funding and working longer careers. Younger researchers, without funding, simply leave the field, as the old eat the young for breakfast.