Prosecutions that are unreasonably delayed often have more cruelty than justice in them; defendants may have lost access to evidence to disprove stale prosecutions, and with the exception of the abilities of new technologies such as DNA identification, if a plaintiff has a good cause of action they should pursue any claim with diligence and timeliness.
The Charging of Max Clifford for alleged offences committed between 29 and 47 years ago brings to mind several similes which I cannot lawfully share with you, this matter now being sub judice and any comment a contempt of legal process, so please be careful if you leave your own comment.
The attempts in Germany to charge and jail 50 men who are thought to have served with the SS-Totenkopfverbände before they die of natural causes is an even more extreme example of justice delayed - in this case some 69 years after their membership, there being no actual evidence of any offences on which basis to charge them.
My own view is that a 15 year limitation for prosecution of the most serious offences is appropriate, with a 5 year limitation on minor offences. But then I also believe that we will all be judged and have to answer for our lives.