Hi, Michelle. Thanks for popping in.
It's not all teenage boys. In fact, over half of roleplayers are 19+. About 20% of role players are female, so you're not quite alone out there. Usually, that means about one woman per group, though, so you're definitely outnumbered at the table.
Checking your local game stores is a great way to start. Most of them have virtual or real bulletin boards to help players get together. Many of them also have game rooms, so you can meet in a public place before you head over to someone's house, or you could play there at the store if you want.
Ask your friends. About 15 million people either play now or used to play RPGs. A lot of people do abandon the hobby as they get older and develop responsibilities, but once they level out those things (the kids can feed themselves, the job becomes part of your life instead of your life, etc.) they want to go do fun stuff again. You might already know people who play D&D.
Also, D&D's the most popular, but it's not the only game out there. Depending on your taste, there are games with Asian flavor, gothic flavor, true horror, science fiction flavor, historical flavor--all kinds of stuff.
Go to the Wizards of the Coast store locator
http://www.wizards.com/default.asp?x=findastore and enter your address to find a game store near you. I might even know who it is, since I owned a store and was active in the community of store owners.
You can also try meetup.com. They have D&D groups on their list.
If all else fails, you could start your own group if you really wanted. That takes a bit of work, but players are always hunger for somebody to run a game. I played a game one time, and then didn't play again for about 14 years, since I ran the game from my second session on. Obviously, I love it.