I was thinking about Jazil passing...the 2006 Belmont Stakes winner...and it reminded me that Bernardini is the only remaining Triple Crown winner from 2006.
With the passing of Deputed Testamony, Hansel became the oldest living Preakness and Belmont Stakes winner...he won both in 1991
http://www.bloodhorse.com/horse-racing/articles/84530/catching-up-with-hansel
Is he the oldest Triple Crown winner?
Yes.
However, the oldest Kentucky Derby winner is Sea Hero who stands in Turkey.
Go For Gin who can be seen at the Kentucky Horse Park is the oldest Kentucky Derby winner in the US.
http://www.bloodhorse.com/horse-racing/articles/84523/catching-up-with-go-for-gin
I also think of some of the horse that passed before their time...
Barbaro (2006 Kentucky Derby)
Summer Bird (2009 Belmont Stakes)
A.P. Indy would be the next oldest Triple Crown winner having won the 1992 Belmont Stakes, the year after Hansel.
Also, Editor's Note, the 2004 winner is in Argentina...
Victory Gallop, the 1997 winner, has moved on to the Jockey Club of Turkey.