Have you ever seen someone in their 40's or 50's struggling to lift something you think is light? Have you seen a 30 year old out of breath after climbing 1 flight of stairs?
Of course there are good health reasons why this happens sometimes, but usually this is a sign of someone neglecting their health.
Here are a few quick tips to make sure you're on the path to longevity.
Count calories.
I'm not saying you need to count every calorie for the rest of your life, but I am saying you can't get obese if you know what you're eating. Calories in = calories out.
Exercise daily.
I don't care what you do, but do SOMETHING. The human body doesn't respond well to sitting all day every day. Go lift weights, hike, walk, play with the kids, whatever. Mix it up but keep the exercising consistent.
Track metrics.
I know that I have cancer and heart disease on both sides of my family. I believe most of that was habitual and not genetic, but I can't prove that. What I'm saying is that you might have family history, and it might not matter, know your basic numbers. Get some basic equipment: scale, pulse oximeter, heart rate monitor. That will cost you $50 or so. Heck, set up a yearly checkup with your doctor. Do something to avoid surprises.
It's really easy to keep your health in check. I promise it's only daunting because you don't know how it works yet. Once you develop the habits, it's second nature. Plus, your future self will thank you for the the savings in health bills later.