You appear from your published CV to be much, much younger than 51. I'm not 51, but I'm much closer to it than you are, and at an age where many people in my social circle at past that. What on earth gives you the confidence to say something like "at 51 you don't have the energy to compete"?
Also, at 51, you probably have more time to compete than a 36 year old.
I think you're way off on this.