Body is not stiff, mind is stiff.
Yoga is an internal practice. The rest is just a circus.
The full ashtanga system practiced with devotion leads to freedom within one's heart.
Yoga is your mind control capacity.
Anyone can practice. Young man can practice. Old man can practice. Very old man can practice. Man who is sick, he can practice. Man who doesn't have strength can practice. Except lazy people; lazy people can't practice Ashtanga yoga.
Do your practice and all is coming.