mrv You don't even need to go through the trouble of removing the crankset or chain, just the pedals will do. We started the kids off with a balance bike because it was smaller and light, but to transition to a pedal bike, I took the pedals off and kept the seat low enough for them to use the 16" bike as a balance bike. Once they could balance at speed, we put the pedals on and started with "push down hard on your front foot after a little push with your other leg".
ropetwitch I learned late for my generational cohort, at 10. It was only after I got a purple hand-me-down from my older cousin with unreliable training wheels that I even tried. I tried to learn on grass in the yard out of fear of scrapes, but it wasn't until I risked pavement that I was able to start riding. If you insist on learning to pedal and balance at the same time, find a disused parking lot and wear a helmet. Keep your feet on the pedals and hands on the handlebars if you go down and try to absorb the impact with your entire side instead. Trying to ditch the bike entirely during a fall is actually hard. I wouldn't recommend trying to learn on a road frame because your intended posture doesn't jive well with pushing the bike with your legs while in the saddle. Try a cruiser or hybrid first, and make sure the frame is sized so you can lower the saddle enough to plant your feet on the ground. This is likely going to be one size down from your size on those bicycle fitting charts.