Nice idea, but I assume anyone recruiting for space travel is going to insist on people who are very fit and in 100% good health, which usually means fairly young people. Certainly there could be some older people, but probably not a majority.

Which is why the ISS is populated by PhDs in their 40s?

Of course you want the first colonists to not be sickly, but they won't need to be Olympic decathletes in their 20s. Equipment for lifting heavy objects can be sent more cheaply than people (it can go slowly and doesn't need life support).

I think for a venture like this maturity and patience is going to be more important than physical strength. There will be a lot of tedious tasks with long checklists that need to be followed near exactly to succeed. There will be a lot of disappointment and frustration when things fail or timelines slip. There will be the irritations of being stuck in a small social circle with a few people you intensely dislike but have to depend on for survival.

Add in the fact that your sperm or eggs will probably get exposed to large doses of radiation until they figure out how to get to Mars faster, and it will be far less attractive to anyone who is planning to have kids someday.

With substantially less gravity, you can lift 2.6x the weight as you can on earth. People in their 40-50s in good health with moderate strength, good maturity, advanced skills, and already-grown children are good candidates. And yes, with the radiation they'll get hit with, it's better than kids burning away their lives.

> There will be the irritations of being stuck in a small social circle

in my own personal experience, this thing works worse for older folks, who get territorial, grumpy and so on. But we aren't discussing folks in their 40s, rather 50s and 60s