If you have exercised in a long time the most important thing is to be realistic about what you choose to participate in. This is not to say don’t try different, new things it just means don’t jump in over your head and take on too much
Choose something really fun (i.e. riding a beach cruiser, with a banana seat and tassels), start off with 15-20 minutes and add a little more each time. Deciding to train for a marathon in 4 weeks if you’ve never run is probably not realistic. It’s probably so unrealistic that it actually sets you up for failure, decreases your self-esteem and lowers your motivation for exercise.
Rather than participate in an exercise program that someone else thinks is beneficial for you find out what activities are going to make you happy. Exercise can be fun. It does not need to happen in a gym on a treadmill.