I found a nice game by a 'veteren' Grand Master in Informator 26 which covers the second half of 1978. I put veteren in quotations because Mark Taimanov was only 52 years old in 1978. FIDE have dropped the age for veterens to 50 which means he would have counted (and I will too soon) but it hardly seems fight that 50 year olds should be considered veterens in chess terms. In Taimanov's case, only 7 years before this game he was playing, and famously losing, a quarter final match for the World Championship against Fischer. And in 1978 Taimanov's rating was still a very respectable 2530 which couldn't have made him far off the top 50 in the world, if not being in that select group. It is argued that as players age, their experience counts for more and they become strategically better, which covers up for their failing calculation. This may be the case, but it doesn't mean a 50 year old can't calculate when the tactics are there.
Pretty handy tactics for an old guy? And he played to a pretty high standard for years after this. In fact, Taimanov is still alive, and at 88 I reckon he could still play chess to a pretty high standard. Take a look at a chessbase tribute to him for his 85th birthday to see how young an 85 year old can be.