There are lots of sports that you can take up as a child or an adult which can teach you skills and improve your fitness levels. Karate is a sport that can be taken up and enjoyed by almost anyone no matter what their fitness levels are. Martial arts are more about the dedication that you put into the sport rather than your fitness levels. If you are willing to put the time and effort into learning the sport you'll be able to progress through the sport well and in the meantime improve your fitness levels and general well-being.
The great thing about learning karate lessons is that they are available all over the UK and schools offer different times and schedules, meaning that you can find one that suits you perfectly. It is also a sport that can be enjoyed as a family, if you want something that you can do together and all feel equal when it comes to skill level
If you contact your local sports centre or martial arts school they should be able to give you advice on where to start and what you need to get started. If you are not sure of anywhere local that offers this then looking online is a great place to start. Of course just searching for something along the lines of karate lessons' isn't going to do you much good. This will return results from all over the world and so is going to take up too much time to go through them all and find one relevant to you. It is far more efficient to simply add the name of your area to the search, so search for karate lessons Gillingham' for example. This means that the results you get are much more tailor made to what you are looking for and it makes it much quicker for you to find lessons that are going to suit you. Most of them have their lesson times online so you can easily compare then and find the one that is going to best fit in around the commitments you already have.