So, there are a few parts to improving flexibility (or more importantly, mobility). Stretching alone using static stretches is only one way and one component. We can also use dynamic stretches and strengthening exercises to help improve mobility around joints.
It does get harder as you age, especially if you have not been using good range of motion for a period of time.
You could start by doing static and dynamic stretches and the strengthening exercises shown in this video 3-4 times per week. Aim for 30seconds hold with the static stretches and 10-20 reps for dynamic stretching and strengthening exercises.
source