"I think ten years after the crime is, for the most part, a reasonable "statute of limitations.""

There are often people being prosecuted for serious crimes they've committed in the past whether it is major crimes against humanity or more likely ordinary murders etc. Are you really suggesting that if a child is murdered and the perpretator is either not found out for 10 years, or is found out but evades justice for 10 years, then they should get off with it? Or to your other point that someone over the age of 80 but still of sound mind shouldn't be treated exactly the same as a younger person? I find that pretty hard to grasp.