I doubt that age is really the issue. Nothing in WoW requires real twitchy reactions. My guild has a number of people (myself included) in the 35-50 year old range and we don't find ourselves running into any unusual difficulties.

Could it be that the younger kids have better computers with faster framerates? Perhaps they have better keybinds than you so that they can watch the screen and move/attack more readily. Maybe that particular skill reminds them of some other games they played that you may not have.

In any case, I'm sure that with a little practice you'll figure it out.