I promise to NOT do any Polar Bear swims. Bet I can keep that one.
Should people start any of the activities that I do? Each has positives and negatives.
Running is a good one. Great exercise and a challenge to one's willpower. Sometimes it is very hard to hit that road and get the miles done. It can also be very hard on joints. It also needs serious footwear that doesn't last very long.
Biking isn't so hard on the joints and is a better method for actually getting places. It does require a bike, which is a major capital investment. Like running it can be hard to get motivated on crummy days.
Karate can be good exercise, but can also be the opposite. Joining a group that pushes too hard is worse than not joining any. I'd advise watching a class before joining. If they won't let you, just thank them and leave. Probably not the right group. Is everybody young? Not a good sign. Do they wear uniforms other than white? Leave.
Jiu-Jitsu can be a good choice. Any of the Brazilian forms are great for the young, but I especially recommend Gracie Jiu-Jitsu for the mature participant. It is non-competitive, which means nobody trying to really dislocate your bones.
If you live on the Sunshine Coast of BC, and are any of the adults who sometimes reads this blog, and if you might want to try Gracie JJ at the Gibsons school please give it a shot. I'll be there and be happy to be your partner. It takes a while to get limber, and having somebody that really understands this would be nice.
Or maybe a nice PolarBear Swim is more your style.