I am 37 and I want to say I started at 7 or 8 so almost 30 years ago, maybe more. As the tale goes, one day My Mom bought a model kit for my dad as a present when she saw them at the local dug store, perhaps as a birthday present. this would have been in 82 or 83. My dad had built models as a kid. ?He started out brush painting everything then started using spray paints and a badger spraygun with air cans. We would go to the National air and space museum and buy a model of an airplane we saw My Dad also taught me about all the different airplanes this way. At some point along this time I was given snap tites and simple glue models and my dad would help me. Later on we got an airbrush, compressor and a spray booth, and eventually when I was in High School oh say 9th grade or so I was airbrushing on my own. My parents were always pretty supportive of the hobby.
We usually had the latest issue of Fine Scale Modeler around the house. My Grandfather on my Dad's side built ship models, and my Uncle on my Mom's side built planes, then switched to race cars. He turned me on to NASCAR modeling and the Model car magazines of the time in the early 90s.
I never really stopped, I did not have much time when I was in college, I lived at home but much of my free time was used up with Radio Control Cars, studying, girls, etc but I never stopped completely. I have always built a mixture of Cars and airplanes. Once I was done with school and working full time in 1998 or so I returned to the hobby with more enthusiasm and attention to detail. I built quite a few models in the early 2000s but they all got damaged in a move and I tossed them. I build at a glacial pace these days but I enjoy it.
Now That I stop and think about it, it really runs in my family.