Can anyone do karate? Well, absolutely, and I think this is what distinguishes karate from so many other sports and martial arts because as a small child you can practice for balance and coordination and these things. As a teenager or in your twenties, you can practice in a very dynamic way of giving full expression to speed and power. And, as you get older, you can simply refine your technique. Unlike some other arts, there's no necessity to be thrown or throw other people or any kind of contact. There's no necessity for a partner and so you can practice if you are young or old.
I have six year olds. I have someone who trains regularly with me who is 75. You don't need to apply karate in the same way at any age. You can apply according to your ability, according to your age, according to your desires, and even according to the day. Some days when you're feeling very aggressive it's nice to release that. Sometimes when you're feeling templative, it's nice to have a gentle session. So, karate covers all these aspects.