Wow, good question. I'd say 11. I was a kid in NYC, had lifelong friends, lots of family around (including my grandmother with whom I was very close; she died the next year), the Yankees were on the way to their first pennant in my lifetime, I got to go to a baseball game at Yankee Stadium for the first time (it had been closed for 2 years for renovations), a World Series game, my first card show (Thanksgiving weekend ASCCA show). It was the Bicentennial and there were celebrations and events all summer. My family spent most of the summer in a village called Mahopac in the Township of Carmel, Putnam County, NY. I remember it as a very happy time in my life.
A view of Lake Carmel: