You need a plural s here in year! What justification do you have for not making year plural? How is it different than "I arrived in 60 minute"?- In all of the cathedral's 800-year history
Story might not be a good example, for some reason I never seem to see the use of the word for building height pluralized.Would you also say "a 10-years old child" and a "50-storeys building"?
But I think I might see your point about "a 10-years old child", it does look slightly odd, but I can't say why. Maybe because there is a singular "a" right before it for the child. Still, that should be right, or if it's wrong, please explain to me how, and why. Especially, what purpose singular serves for talking about more than one of something, how does it better lead to understanding?