Impossible Dreams. I like numerically-themed writing prompts, but never considered any integer larger than 10.
(Apologies if I took the theme too literally.)
Pity the reputation of the number '50'.
It is a middle child, used to indicate the halfway, the median, and the demi. As every student and teacher knows, 50 is poised in this middling yet crucial position between success and failure. As every employee knows, 50 is not quite retirement age, and every senior citizen knows it is not yet the signpost to the land of the second childhood. 50 cents is only half a dollar or a mediocre rapper.
50 has a smaller sibling called 5, who has more esoteric and biological associations. There are 5 elements, 5 points to a star, and amphibians, reptiles and primates (including us) possess 5 fingers and toes.
But 50 refuses to be upstaged- it manifests in geography- (50 states in the USA), and two 50s in the same sentence, 'fifty-fifty' denotes equality.