It is not a guarantee that their old age will stop gambling, because gambling does not require energy to do it. So, when those who are old and still have capital or money, then of course they will still be able to gamble at an old age. Because the point is,age will not be a guarantee for anyone to stop, because those who stop gambling are not because of age but they have other reasons that strengthen themselves to stop or continue gambling. After all, gambling itself can start at a young age and also, many young people who previously gambled but they chose to stop quickly. So, age is not a reason for them to stop gambling, but another reason that will make them really stop gambling completely.
Consider also that when you are already in old age, you don't have much to do in life. So one way to get your mind busy is to do something light, like gambling. Hence, some old people are devoting their time into this laid-back activity. It doesn't mean that they will spend good money to this, but usually it is just to pass their time. So they are only allocating whatever funds they have.