What’s your favorite way to workout? Weightlifting? Running? Maybe aerobics classes? The best way to stay in shape for the rest of your life is to find the activity you enjoy the most, and stick with it. For some people that might not even be setting foot in a gym, it might be playing sports or hiking.
The best thing about going to a gym though is that you can measure your results. If you want to make consistent progress, you need to know where you’ve been and where you want to go. If you don’t know how fast you can run a mile, how do you know you’re getting any fitter playing your sport? The same thing goes with weightlifting–results need to be measured consistently so that you can figure out when you’ve hit a plateau, and then do something to break through that.