In my experience the older students respect you more, and listen to your advice carefully. I've never had a problem telling someone twice my age what they were doing wrong.
The students to watch are the 15 - 17 year olds who are avid flight sim experts. A rare few of these thinks they know it all, and if they have some natural talent to back this up their confidence soon surpasses their ability. Sometimes, these need to be brought down a peg or two by applying the pressure a bit, or a particularly pronounced stall recovery to show things will bite if they don't pay attention.
On the whole, it's an absolute joy, whether it's someone's first experience on a trial lesson or sending someone solo.