So I eventually found myself at 30, after a decade of software engineering work with a metabolism that started slowing down. I stopped being able to automagically disintegrate various candies and snacks that I'd often eat while working, having developed the habit during my college days. I started noticing my stomach getting bigger, particularly when I was sitting down at my computer, and concluded I needed to do something about this. So, I joined a gym and started working out.
My exercising and working out has varied quite a bit over the years that followed. I've learned a lot about my body and what it can and can't do. I have had some success in working on my upper body, despite decades of doing nothing but lower body work (track/cross country/marching band), though I've got a ways to go to get to where I'd like to be. I've dealt with and come back from a couple of scary (to me) injuries. [Side note - never try to use P90X as a mass building program - you'll get RSD and rep-related injuries once the weights get high enough]. I've increased my overall strength such that marathon sessions playing my bass saxophone (e.g. at Picnic Day at UC Davis) doesn't result in debilitating soreness for days after.
Exercise is a great reminder for me that life is a journey. Each time I work out I strive to do a little more than I did the last time. I celebrate the successes and let go of any failures, as temporary setbacks are just that - temporary. It is my hope that what I do now to try to maintain myself will allow me to continue to be able to do the things I love to do and to be healthy for my fiancee, my children and perhaps someday many many years from now my children's children.
Find something physical you love to do and just do it. Everybody exercise!