I am considering starting refinishing business. My friend who is in the business stated that it would take about a year to learn how to refinish floors. Please give me some thoughts on this

No way! you can learn how to refinish a floor in a day, Perfecting it and makeing someone pay for your job well that's a different story

My wife and I have refinished some floors when water based finishes were fairly new. The sanding work is the hardest part, but anyone can do it if they are careful. The finishing was a snap, really. We used the foam pads on a long pole to apply it. Looked great, and our customers were happy.