It isn't just about cracks, tires continue to vulcanize (get harder) their whole life. I bought a brand new, 5yr old Dunlop that had been stored inside on a rack and was hard as a rock, caused the front end to wash out on me on a 20mph corner. It's up to you to feel the rubber and see if it still has good grip.
2007 V2K, Pearl White/Ti, Road Burner 3", Fi2000, Euro gears, Double Darkside (totaled 4/25/15)
1998 STX 1100 JETSKI (HERS)
1996 ZXi 1100 JETSKI
1982 GL500 SILVERWING (sold)
1983 JEEP WAGONEER