Yogis don't live forever. I suppose a few folks take up Yoga with the misguided notion that they can find the perpetual Fountain of Youth, but that is not what Yoga is about. Life itself shouldn't be about trying desperately to find immortality either.
If you come to Yoga with that goal of staying forever young, then you miss the joy of growing older. I don't mean getting "old". The operative word here is "growing". Reaching new heights, finding new depths, developing real wisdom, none of which can happen if you dig in your heels and try to stay in your youth. Some Yoga poses may no longer be available to you, but others will bloom. Meditation will become easier and finding that quiet space in savasana will become much easier.
In Life and Yoga, if we either live in the past, trying to cling to it, falling prey to Attachment, or we turn away from a future where we will grow older, falling prey to Avoidance, we lose the only time we have ... Now!!!