What happens after we hit 50, is a decline in performance. A decreasing aerobic capacity, loss of muscle mass and an increase in body fat. There are ways to slow the changes or even reverse them. Not huge changes. What we as runners need to do are small changes that will postpone the changes in our body. If we start to train and live smart we still will be able to run fast and strong after 50.
I'm 52 and just a few weeks ago I ran my marathon PB and about 6 months ago, just before I turned 52 my half marathon PB. If you ask me it's possible to run fast after 50 but you need to be smart about your training, nutrition and recovery.

In case you need a training plan fitted to your age all you need to do is to contact me over the contact form on Run&Smile and I will get back to you.