My husband is 23 and I am 25...we are swingers. I think that the question itself is an interesting one. You see, swinging is dangerous for a lot of people. If your relationship is such that you don't communicate well together then it is dangerous. If you aren't completely honest about how you feel or what you are thinking then it is dangerous. It doesn't matter if you are 25 or 45. There is a need for some maturity, but maturity has never been something dished out according to age. We often look at the world and figure that the older you are the more wisdom and maturity you have gained. However, we have all met older people who are immature and younger people who are more mature. It just doesn't always work according to age.
Now as young swingers we do have a few disadvantages. First of all, our kids are young. This can make swinging a bit harder then it would for those who have more independent children or those who have grown children. We can't just leave for all night trips or visits at other people's houses. It can also make it harder with the babysitter!
Additionally, the majority of the swingers that we meet are older. This can cause some age issues. We have always had the opinion that it doesn't matter since we aren't looking to get married, but some couples have a hard time enjoying the company (especially in more intimate settings) of people who are lots younger or the age of their children.
So, while being a swinger at a younger age can have its challenges, it isn't much different from being a swinger at an older age. There are also a number of reasons that the swinger community tends to be of an older demographic.