Not really, I am learning them in Yoga now and I am 37. Its muscle memory, you have to start slow and make sure you don't injure yourself. You are definitely more open/flexible when you are young and can learn it a lot faster, but as an adult if you take your time, you can still do it, if that's your goal.
It's where u stretch to do them often that makes u able to stretch further so it more comfortable
Are you reading my mind!?!
It is absolutely possible. From my experience, the only difference and the major advantage to stretching and training when you are younger, is that your recovery time is so much quicker. You need to allow for more recovery time as you get older, which means that the progress will take longer.
But it is definitely possible!