Football season for semi-pro players generally starts around April and ends in July. Most teams rent playing facilities such as high school stadiums, so they can't play when the school needs the field for its own schedule. Teams in areas that have hot summers may start their seasons a little earlier.
Most require players to be 18 or older to try out. They don't have age limits though -- some teams have players who are into their 60s [source: Bouchard]. Also expect to sign a waiver that proves you have your own health insurance.
While each league sets its own schedule, look for tryouts during the winter, particularly in December or January. Some semi-pros may even offer pre-tryout training opportunities to work on weight lifting and general conditioning.
What kind of training should you do before tryouts? Start here by dialing back to the end of summer.