The good news is that you can improve your flexibility starting at any age. The body is remarkably resilient, as long as you pay attention to your own comfort levels, go slowly and be consistent. Some of the most rejuvenating stretches can be found in yoga. Ballet exercises are another excellent way to develop flexibility, and there are plenty of basic sports stretches for hamstrings, leg and upper body areas. Warm up first.
Tight muscles are more forgiving when warm.
March in place, swinging your arms vigourously, for a few minutes to get the blood flowing. It's useless and can lead to muscle tears and injuries. Stretching is most effective when you go as far as YOU can go, then hold the position gently for a few moments. Release it, then stretch a second time. You should feel a sense of lengthening, not pain.