I started riding on a 2.5 HP tote gote at age 10, and got my first real motorcycle, a 185cc Suzuki at age 14. I started riding ATVs at age 38, on a Yamaha Kodiak 400. I now ride a Renegade 800, and a KTM 505 XC-F.
My oldest son started riding a Honda XR 70 at age 7. At age 8 he won an award at the Rocky Mountain ATV Jamboree for being the youngest rider to be out riding the Jamboree trails on his own ATV, which was a Honda TRX90. He rode his TRX90 on a trail that was 120 miles long, and rode it through a pouring down rain storm that day. He now rides a KTM 300 XC dirt bike, and has won the open class at regional desert races.
My youngest son started riding a Polaris Scrambler 50 at age 4. He is now age 13 and rides a Raptor 250, and also competes in regional desert races on a KTM 85 SX.
My wife started riding at age 33, on a Yamaha Wolverine 350. She now rides a Yamaha Grizzly 700.