One of the asymmetries in the races for the two parties’ presidential nominations is generational. The Democratic field of candidates tends to be relatively old, the Republican field relatively young. The following table shows the names of the candidates born in each year from 1941 to 1971.

The average birth year for the Democrats is 1950, just four years later than the 1946 birth years of Bill Clinton and George W. Bush and 11 years earlier than the 1961 birth year (in Hawaii) of Barack Obama. Three men currently mentioned as possible additional candidates — Joe Biden (1942), John Kerry (1943), Al Gore (1948) — have birth years even earlier than that average. The average birth year for the Republican candidates is 1957. But only one, Rick Santorum, was born about that time. Otherwise you have a Republican generation gap, between 10 candidates born between 1945 and 1955 and six candidates born between 1962 and 1971.