It Can Be Hard to Do Little Enough
We all know that exercise is important. Equally, we all know it's hard to get started. When you're just starting out, one of the most important things — and one of the hardest things — is to not do too much.
My dad is 80 years old. He's overweight, has a heart condition, and is generally in terrible shape. Probably once a month he says, "I should start going to the gym". To be honest, he shouldn't. On the very rare occasion that he actually goes to the gym, he ends up not being able to leave his chair for a week. For him, he should walk to the end of the driveway and back, and he should do that every day for a month. Maybe only every other day for the first week. Then he could think about doing more.
For most of us, our condition isn't that bad, but the lesson still holds. I can't tell you how many times I've had friends jump into the gym in their 30s or even 20s, hit a "light" workout, and end up nearly incapacitated for a few days.
When you're young, the incapacitation itself isn't the issue. You'll recover in a few days. The issue is, if it's bad enough that it knocks you off your track for 2-3 days, then there's a very real chance that you don't get back to the gym for another week ... or two ... or ... ¯\_(ツ)_/¯
When you're just starting out, or just getting back into things, whatever you think you can do — do less. And then do it again the next day. And the next.
It's far less important that those first few workouts be strenuous than it is that you make the work a habit.