Go for it! This is something that I have been thinking about. But location is very important, stay away from very large cities, because there will probably be a lot of competition.
Tuners make great money. Where I am from, they charge about $100 to tune a piano. The population in my city is about 300,000. I believe there are 4 tuners.
But do your research and make sure you become a certified piano technician.
There are many scams out there, where one can become a tuner from watching these videos. Look for a college program, where you will get hands on training.