A lot of people give the age, weight and so forth when what matters more is your budget, what weight range you want to carry, the comfort level you're striving for, where you want to go, and what weather conditions you expect to encounter. That has a lot more to do with the gear choices than anything else.

You may not know what weight to expect for backpacking gear... look at Mark Verber's site, and read the gear lists and articles on the main page of this site, and keep reading forum posts. Rent and borrow gear. Find a hiking group in your area and talk to other backpackers in person. That'll also give you people to borrow from. Get sized for a pack, and start looking at weather forecasts in the areas you want to visit, get an idea of expected night temps, etc.

ETA: Beware REI syndrome. Newbies who rely on the outfitter to give them what they need will show up with much, much more than they need, and quickly figure out that 50 lbs is not quite ideal. A basic gear list from this site and a good look at trailcooking.com will help you sort that out a lot more cheaply.