Depends on where you plan on riding. If you wanna ride on the roads than any bike will do as long as it fits you. I would stray away from suspension-less bikes, but it depends on how you like to feel during a ride. Personally i think the genesis v2100 is one of the best beginner bikes. It pedals smoothly and is only bout $160. And you can find it at walmart. I have had mine for 2yrs and it still rides like a champ.
Never too old to ride a bike.<br />
I agree with UFO, get a second hand or cheap bike.<br />
I highly recommend cycling, my favorite way to travel! Since you're just starting, don't spend a whole lot. You can easily walk into a bike shop and drop $2000 on a bike that's gonna sit in your garage if you decide you don't like cycling as much as you thought you would, or you don't have time, or whatever. My advice will go against what most of the "bike pros" are gonna tell you, but after all, you're not trying to win the tour de France, and bike pros only get rich from selling expensive bikes! You just want an inexpensive bike that you can have fun on and get a little exercise, so I say find the cheapest used bike that fits and ride it around for a month or two just to discover if cycling is your thing. You can probably get one for under $50; I bought a bike for $10 one year and rode it all summer! Then, once you've decided you like it and want to keep at it, you can invest in a more expensive bike.<br />
(BTW, Lacie, the brand you're trying to recommend is "Specialized" not "Specialty." And I do agree, they're great bikes; I have an Expedition myself)<br />
UPDATE: you can get an inexpensive bike at garage sales or secondhand stores. Might need tubes for the tires or small fix-ups, but worth it
I love to bike too and it's great exercise (especially if you hate running and jumping around). Last summer I lost ten pounds with biking as my main exercise (though I was swimming too). I dunno if there is really much difference in bikes. Mine is just a multi-speed bike I got at Target for $100.