I've gone smokeless for several long periods. I really did not smoke anything for the first 19 years of my life - so that's probably the longest. I dabbled with wacky tobaccy in my college years, but outgrew it.
After another 13 smokeless years, I was introduced to cigars when I was 36. Since then my longest smokeless period has been about 5 months. This was my transition period between cigars and pipes.