About 15 when my parents bought me a cheapo no-name acoustic guitar with baling wire for strings and that good high action I've seen mentioned above. Talk about callouses! I eventully saved up some money and bought a Harmony Sovereign when I was 18. That was my only guitar until about ten years ago when I traded my truck for some cash and and a couple of electric guitars and an amp. Then I bought my Taylor 310 and pretty much retired the Harmony.
Guitars: Charvel/Jackson CSM-1G, DeArmond M-75, DeArmond Starfire Special, DeArmond S-73, Epiphone Collegiate UK, Squier 51, Michael Kelly Patriot Custom, Harmony Sovereign, Taylor 310, Takamine 12 string, SX thinline, Fender MIM Strat, Ibanez JTK30,
Amps: Earth Sound Research G-2000 Super Guitar head into Avatar G212H cab, Fender Sidekick 20 Chorus, Peavey Classic 20, Peavey Classic 30, Peavey Express 112, Fender Super Champ XD, Vibro Champ XD
Effects: Digitech EX-7, Digitech RP-250