David Hindman's son John-20 missing yrs

John Hindman, son of David and Agnes Linville Hindman was born c. 1760.The next record I have for him was his marriage to Sarah Matthews c. 1801 and then his move to Armstrong County (now Clarion County).John and Sarah had twelve children.
I find it unusual that a man would wait until he was over forty to marry and begin a family, especially in the early 1800's.
I am looking for information that would account for the gap in time.I know many Linville family members moved south, so perhaps that is a possibility.
Please contact me if you have any information on John's missing years, or a John Hindman that cannot be accounted for.