Act like the mature man you are
If there's one thing a woman expects from older men, it's maturity. Using your age and wisdom to your advantage will set you apart from her 20-something peers. Never assume a younger man's game is the way to go.
For example, don't think you have to go out of your way to make your presence known. No matter where you are -- a bar, the beach, the eye of a tornado -- every woman in the room is already fully aware of your presence. Ladies are observant! So play it smart -- no staring a woman down, obviously nudging your buddies, pointing, or making gross comments (ahem, note to all men!). She'll see all of it.
If you want to attract her attention, do normal decent-human stuff like making eye contact and smiling in a non-threatening way. If you do want to approach her, play it polite and open. Don't crowd or leer, and don't make obvious references to her age or body. Keep your introduction short and sweet. Let her know she caught your eye. Tell her you're interested in getting to know her. Offer to buy her a drink.
SIMPLE. If she's interested, she'll reciprocate in her own way.
Be upfront about your expectations
Vague intentions, game-playing, and a lack of communication are just some of the crappy dating behaviors younger ladies have come to expect. Offer her a welcome departure from all that crap by being self-assured, and straightforward about your intentions.
Be honest with her: would you like a simple date? Something more? Are you genuinely interested in pursuing a relationship? Let her know, and see what she says. Older men knowing what they want is hot.
Address the wizened elephant in the room
Don't assume every woman you pursue is A-OK with the age gap. Ask how she feels so you can anticipate possible conflicts down the road. She may be new to dating older men, have her own personal reservations, or not even be aware of how old you are. (In which case, keep doing what you're doing, it's totally working.)
There's no need to make a grandiose statement here, but it's totally appropriate to ask how she feels about the age difference. Just get the conversation out of the way and move on.
Treat her as an equal
She may be decades younger than you, but she's still a legal adult (ahem). Understand that she's been paying her taxes, calculating her bills, and making decisions long before she met you. Like any good partner, you'll feel the urge to offer your advice or guidance where you see fit -- but respect that there are times she'll be open to it, and other times when she will not. The latter is NOT the time to dredge up the age gap, or remind her of your years of experience in X/Y/Z.
Huge power imbalances -- like the kinds that sometimes come with substantial age gaps -- can produce frustration or an eventual sense of defensiveness. If she's constantly feeling like she has to explain or justify her actions, decisions, or personality to you, she'll eventually learn to resent you or see you as a paternal figure -- the opposite of what you want.
Bow out gracefully
Now, say she loses interest. Here too, act like a mature man by not getting mad, upset, or fussy. These things happen, and sometimes it just wasn't meant to be. You'll leave a much better impression by simply leaving things where they are, and thanking her for her company. It's the right thing to do.
But who knows? Maybe with some time and consideration, your last interaction can make the perfect springboard for her to jump right back into the swing of things.
Remember: we love the maturity that older men bring to the table. It makes us feel more comfortable with airing out our grievances, and talking through whatever reservations we might have. There's a 50/50 chance that you can salvage the relationship by speaking to her concerns; but if not, channel a little of what she finds so attractive in you by staying centered and moving on.