I think people often ignore the stiffness they have, or a little niggle here and there and completely dismiss it as a part of life they'll have to live with. But I think most problems can often easily be remedied and one of the best ways to do this and one of the most important things you can do to aid your training, increase performance and reduce your chance of injury is have a look at your biomechanics.
I went and saw Rachfit (a biomechanics coach from this forum) a few months ago. She checked lots of things about me, like flexibility, range of movement, balance, proprioception etc, it turns out, like I thought, I was pretty crap at most of it.
She gave me 4 exercises, that were similar to stretching exercises, but much gentler. The idea for most of them (I think!) was to gently mobilise and free up tethered nerves. I'd tried stretching for months, but wasn't really getting anywhere with it, you'll have to ask someone who knows more, but basically because they were aggressive stretches, they we potentially damaging nerves, so muscles tightened and tethered to avoid injury, this made my flexibility worse. She also looks at kinetic chains and all sorts of things like that. Search the internet for what it all is, it'll probably explain it better than me!
Anyway I'm rambling, after a couple of weeks my flexibility was improving, tight muscles loosened a bit and little niggles in my lower back, shoulder and hips were disappearing and stretches are now starting to work like they should.
That's the biggest difference it made to me, but getting your biomechanics sorted can improve performance, reduce injury, increase flexibility and can basically be very beneficial in lots of ways.
So do some research and think about seeing Rachfit or a biomechanics coach, it could help you a lot.
Website on biomechanics:
http://www.intelligenttrainingsystems.com/index.php