What's the minimum exercise one should do in 30s to stay healthy by 70s?

Imo you need to become awesomely fit and maintain that level for at least a year before your late 30's. I believe this gives your body an ability that it simply never develops otherwise.

I was a serious athlete (and I smoked too) into my early 30's. In fact my fitness level at age 29 was on par with elite Olympic athletes proven by laboratory testing. Fast forward to my early 50's--I had some injuries and truth be told I hadn't worked out for about 10 years.

Two things changed that: a dream in which I couldn't do even 1 pushup, and a bad reaction to an antibiotic which caused nerve damage in my dominant arm. So five years ago, at 55, I started working out again (I also had quit smoking the year before). Today I'm 60 years old, and I can plank for 4 minutes and 30 seconds. I recently did 70 consecutive pushps, and I can do over 60 consecutive situps. I recently (about 6 weeks ago) started running stairs where I work and I can run up over 6 stories at a time--this has increased my core strength by leaps and bounds in a really short time: again a 4:30 second plank time.

As a side note; in the past 5 years I have lost about 33 pounds and I now weigh what I did at 18. I continue to make gains fitness-wise and I feel in some areas I am the strongest I have ever been in my life. I credit this largely to the fact that I was so fit 30 years ago.. and genes I'm assuming play a part in this.

Try to find an activity you enjoy. You will never keep up a sports regime if you don't enjoy doin it. There are so many different effects in long term health, that the specific sports/exercise won't matter.

Also, consider this: Imagine you look back at your life, having spent countless hours on running, and never enjoying yourself.

Find something you can endure long term. Doing exercise will clearly be hard, no matter how you slice or dice it.

For me, it's 40 mins on indoor bike/ 4 times per week, but I do it at really High intensity, so it's really hard core.

To make it easier, I'm watching movies (series) while doing it. I don't think I could have done it otherwise. So, I've done it for about 5.5 years, stopped for almost 1.5 years (leg injury), and now I'm back at it for close to 6 months.

And yes, my plan is to do it for the rest of my life.

I'll take it even further, what's one exercise you should be doing on a regular basis? The Turkish Get Up[1]. It works general mobility which seems to be a giant inhibitor as people get older.

1: https://www.mensjournal.com/health-fitness/the-best-exercise...

Best bang for your buck is interval/HIIT hill sprints. 2 mile warm up, 8x20-30 secs all out, .5-1 mile cooldown. This will get you in the best shape for the time spent. Do some pushups, pullups, body squats, planks. Super straightforward and will get you most of the benefits of quality exercise for minimal time input.

The best longevity exercises are low impact and long duration. Look at health and wellness studies based on the amish. They work all day, but they pace themselves.

1) establish a routine you can stick with - it must be a habit, that you can maintain to 70.

2) they say (you know that mysterious group) you need to take 10K steps a day? I found myself I did about 5 to 6K a day on a normal work day, but weekends if I did 2K it was a busy day. There are plenty of devices / phone apps to help you track this.

3) get started on something

Strength training.

Make sure you squat so that you can get up from couches in your old age.

Make sure you can run at least a mile without getting winded.

Fitness and health is more about what you put inside than how you burn it nowadays. If you have low bodyfat % and is in the normal BMI range, you'll be healthy and fit with just regular exercise (walking/jogging a feel hours a week).

Potpourri of answers. Smörgåsbord of suggestions. Myriad ....

But would love to see something evidence based ;-)

Resistance training. And it doesn't need to be endless hours in the gym. Try following @Mangan150 lots of useful stuff.

I'd say 45mins-1hr of cardio per day, and 3 days minimum of some sort of strength training.

I do cycling nearly every day and bench/squat/deads Mon-Wed-Fri.