Definitely start light. And don’t rush to increase your reps or time or anything like that. Even just 5 pushups a day. Get in the habit and make it a part of your routine, like brushing teeth. Then after it’s something you don’t forget to do, just increase it a little every few weeks or months. Even just 10 minutes is good, but if you can eventually get up to an hour, that would be better. Warm up for more rigorous exercise, do some walking or some pushups. Hell, even just having a daily walk is a great way to exercise especially if you have some good sights nearby.