Happy Birthday to your dad. I think your dad and my dad are alot a like. My dad got me riding at 4. I remember my dad riding an old Montessa, then he moved onto Husquvarnas. He rode Autos, the last one was a 500.
Today my dad is either at the races with us on the weekends or taking Matthew to go practice. He really doesn't have hobbies like playing golf, so going to the track and working on our bikes at 74 is his hobby. He changes oil, tightens chains, cleans filters, and any motor work we need done. Not sure what I would do if he wasn't helping us work on bikes.