Hi Kathy
You need have no worries about fitting in. The others on your holdiay will be there for the same reason as you, because they want to enjoy the destination you have chosen. If you are worried about your age, don't. Age is just a number and the beauty of JY holdiays is that you make it what you wnat it to be, joining in as much or as little in your free time as you please.
As Matt says I am sure you will have a fabulous time and because JY holdiays are addicitve, you won't be able to wait to book again on your return.
Have a wonderful holiday.
Chris