I've ridden sleds most of my pre-teen and adult years, but I'm going with 14 years cause 1998 was when I was diagnosed with an incurable passion for it and have been stuck on it since then.
While I was a kid we had a John Deere 440 and a couple of Scorpion Stingers and I borrowed a Whip once or twice. In 1997 I rode my brother's Arctic Cat Jaguar and was so hooked on sledding that I saved up and bought a brand new 1998 Ski Doo Summit 583. I quickly outgrew that motor and stepped up to a 1998 670. I then modified the Hell outta that sled. Put in a UB big bore kit, twing SLP pipes, Boss Seat, tunnel/rail extension to a whopping 144. Got a Diamond S hood for it and a bunch of lightweight parts. Think I got that sled a light as you possibly could. Rode that sled for years and then moved to a 2005 Summit REV 800, modified that and rode it for 4 years, then got a 2008 Summit REV-XP and ended up totaling it on a hidden boulder in 2' of fresh snow. That hurt. State Farm bought me a 2009 Summit XP and I still ride it.
Sleds that I have owned:
1998 Summit 583
1998 Summit 670
1999 Summit 600 (first year of the ZX chassis. It was the wifey's sled)
2002 Summit 700 (Wifey's sled and it still runs pretty darn good)
2005 Summit REV 800
2008 Summit XP 800 154
2009 Summit XP 800 154 with boost! The funnest sled I have ever ridden.