IMPOSSIBLE TRIVIA:Number of People Having This in Common Tripled in Past 100 Years?

This week on Lite Rock Impossible Trivia, I'm giving you concert tickets to see Seal perform in Ovation Hall at Atlantic City's brand new Revel Casino on Friday, July 20th.

This morning's question:... The number of people who have this in common has tripled over the past 100 years.  Researchers say it may have something to do with older women having babies.  What is it?

The answer?  No one got the correct answer today!  Give me your best guess Tuesday morning at 7:20a.m.