For me Flexibility is one of the big exercises for doing Martial Arts and for general fitness, especially if you are getting older.
I started Martial Arts when I was 16 years old after watching all the 80s Classic Martial Arts Movies.
We stretched in my Club that I trained with but never stretched enough outside of the club, sure some days I would but it wasn't CONSISTENTLY!
If you really want good flexibility you need to stretch twice a day EVERY DAY!
Again it all depends how flexible you are at the start and your age.
I struggled with lots of problems as a kid, with having Asthma and my bones not forming correctly due to a lack of Calcium and not training and stretching enough I was very stiff upper and lower body.
I was never Consistently doing stretching until Jan 2016, I started my plan of stretching twice a day everyday with maybe a day rest depending how my body felt. I motivated myself with watching other successful people who were very flexibly. My flexibility was average with all the training over the years but really wanted to be able to hold my leg 180 and do full box splits.
I am now into Feb 2017 and my progress has been amazing, and have a goal for May 2017 on my 45th birthday to do full box splits, as I say age is just a number.
I am making videos on stretching and will have videos on Youtube on our clubs channel Edinburgh Taekwondo
Keep yourself motivated watch videos and read about other people who are successful in what you are looking to do and you will meet your goal