I second the others--at 23 years of age to be thinking about these things--you're way ahead of the game. I think the military is a good career choice as far as providing for a secure retirement (especially now since they're talking about vastly changing it, but you're grandfathered in).
My one piece of advice to you: if you really want to make the military a career, become an officer if at all possible, even if it means changing branches. The salary and pension gaps between officer and enlisted are HUGE. At 20 years, a typical enlisted is an E7 making under 4K per month. The pension at that point is worth about 26K per year. After 20 years, an officer has usually made it to at least an 06. An 06 at 20 years makes 8800 per month and the pension is around 60K per year.