Let us say that the punishment for murder in the first degree is always a 50 year jail term. A man who is 75 years of age is charged with two murders and convicted.

1. At 75 years of age, he will not live to be 175

2. The law dictates that the punishment per murder must be 50 years

3. He's been convicted of two murders, and must have both charges applied to him unless we are not to expect punishment for one of the victims.

Ergo, he must have a term much longer than his lifespan.

There are a thousand details I just skipped over (concurrent sentances, multiple crimes commited in the same act, stacking versus non-stacking offenses, etc) but this isn't unusual and is a perfectly rational and sane outcome.