Sure they do, however not in the same way younger guys do. For older guys they're thinking is more involved then just sex. And when it comes to sex they're more into their partner and their partners needs than they are them selves.
Women, on the other hand, tend to find men a year or two older than she is to be the most attractive, until she is in her 40s, and then it starts trending younger, until around 50 when she finds men a couple of years younger to be most attractive.
A great deal of this is based on biology/reproductive strategy that has been programmed into our instincts by Natural Selection. Younger women near the beginning of their fertile period are the most attractive because they have the greatest number of child-bearing years, while men lack a biological "expiration date" and also tend to build more and more resources over their lifespans.
Assuming he still had a healthy level of testosterone in his system and therefore a sex drive. Then yes, yes they still get turned on by younger women. Tastes differ however. I'm only 25, but a lot of 18-19 year Olds to me just look like kids and I don't find them attractive in that way. But every now and then you'll see a younger woman that turns you on. I imagine it's the same for guys in their 50's. Not all younger women turn them on, but some do.