That old "subtract your age from 220..." is not correct. It is based on no research at all and is really just lore at this point. If you want to truly know your maximum heart rate and aerobic zones, get VO2 testing done. That is expensive and most don't want to do it. It has been shown through research that if you can talk, you are still aerobic, and if you can't, you're anaerobic. So you should do intervals where you are breathless, and then back off to a level where you are working hard, but can speak (aerobic zone). Also, many polar watches will do a cheap and dirty VO2 test. 30-60 minutes of aerobic workout regardless of the type is all you need for basic fitness.
Remember to have fun!