There seems to be some confusion amongst many of all ages regarding how and when it's appropriate to ogle women. I thought I'd take the opportunity to clarify this issue.
An older man must be very careful when checking out a younger woman. If caught ogling a woman (or worse yet, a GIRL) who's considerably younger than him, it is considered very very creepy. It's extremely offensive to the woman he is ogling and I have even seen other men appalled by this behavior. The sole exception to this rule is extremely attractive older men. The formula is that the larger the age difference between the man and the woman he's staring at, the more attractive he needs to be not to get outright slapped. For example, Mel Gibson can leer at the likes of Angelina Jolie, and she may be flattered. However, he would still be considered a dirty old man for looking to long at the likes of Miley Cyrus.
There are similar formula for giving the once-over to a woman your own age. The ratios are as follows:
Handsome Guy : Hot Gal = Not Offended
Handsome Guy : Marginally Attractive Gal = Flattered
Handsome Guy : Unattractive Gal = Ecstatic
Marginally Attractive Guy : Hot Gal = Unpredictable Reaction
Marginally Attractive Guy : Marginally Attractive Gal = Not Offended
Marginally Attractive Guy : Unattractive Gal = Flattered
Unattractive Guy : Hot Gal = Slappable Offense
Unattractive Guy : Marginally Attractive Gal = Slappable Offense, especially if her friends are around
Unattractive Guy : Unattractive Gal = Slappable Offense, because even an unattractive girl wants good looking guys to check her out
Now these principles vary greatly when it is a younger man eyeballing an older woman. An older woman almost always welcomes the gaze of a younger man, regardless of age or level of attractiveness. They say ladies are like a fine wine and only get better with age, but it is difficult for a woman to believe that about herself. Therefore the appraising eyes of a man (or BOY, yikes!) who could just as soon be oohing and ahhing over a fetching young co-ed is very complementary.
This graph should help.
Again, there's a bit of a gap but much less extreme. Example: A super-hot 40-something might still find it off-putting to be glared at by a homely youth but she'd have to be exceptionally striking and he'd have to be either prepubescent or really REALLY ugly.
There's one exception to all these rules for men in a position of any authority, or even seeming authority. It's simply not cool and sometimes illegal.
The moral of this story. The older men get, the more surreptitious they must be when stealing glances at the ladies. And really, as subtle as men think they are, they should be subtler, because ladies notice and it's weird. Young guys should follow the same advice in regards to younger women or women their own age. But when it comes to the maturer selection of the gentler sex, they can have at it! Look all they like while they can...because they are getting older too and before long it'll be creepy.