Our complete purchase history:
1982 Nissan Sentra bought new, sold in 1994
1986 Dodge Caravan, bought used in 1987, sold in 1997
1994 Geo Metro, bought new in 1994, traded in 2002
1996 Mercury Sable wagon, bought used in 1997, traded in 2002
2002 Hyundai Sonata, bought new 2002, sold in 2011
2002 Hyundai Elantra, bought new 2002, sold in 2015
2010 Hyundai Elantra Touring, bought new 12/31/2009, only has 22,000 miles on it.
So, it looks like we keep the cars we purchase for about 9.5 years, on the average.
There were also 3 cars that we were "gifted" with from various family members. The less said about those disasters, the better.