My dad is proof that you can start yoga at any age! He is almost 64 years old and recently overcame a life threatening illness. He enjoys going to Yin classes. Personally, I think he likes it to meet the ladies. He even went to a few power yoga classes with me! He is waiting to build his strength up before he goes to those again. He told me that yoga helped him during his hard days. Doing small exercises and stretches helped maintain his mental and physical strength.
Most studios also offer courses for young children as well. The studio I practice at in Sacramento allows kids to practice alongside their parents, which is probably really nice for parents who may not have anyone to babysit.
Yoga is for everyone! My cats even do yoga, like the cat in the photo!