I think I'll win this competition 
54.2 years over 13 bikes my 1937 Humber and 1939 and 1944 Elswick - Hoppers drag it down but my Brompton is my newest bike and I guess it is about 10 but it is only an educated guess as I bought it second hand.
My 1992 Townsend mountain bike which I bought as a teenager remains the only new bike I ever bought and it has been re-purposed as a touring bike. It and my '75 Viscount Aerospace are my most used bikes.
I have only included the bikes which are currently usable. A 1983 roadster will soon return to the road and I have a 1970s 531 framed Viking and two early 1950s Raleigh Roadsters to fettle in due course.

54.2 years over 13 bikes my 1937 Humber and 1939 and 1944 Elswick - Hoppers drag it down but my Brompton is my newest bike and I guess it is about 10 but it is only an educated guess as I bought it second hand.
My 1992 Townsend mountain bike which I bought as a teenager remains the only new bike I ever bought and it has been re-purposed as a touring bike. It and my '75 Viscount Aerospace are my most used bikes.
I have only included the bikes which are currently usable. A 1983 roadster will soon return to the road and I have a 1970s 531 framed Viking and two early 1950s Raleigh Roadsters to fettle in due course.