I'm still amazed how young Jackie Stewart (74) looks, and (and I realise the accident had a lot to do with it) but Nikki Lauda I thought was late 70s early 80s. He's only mid 60s.
So yeah 1964 F1 Champion John Surtees (80), and then 1969 F1 World Champion Jackie Stewart (74) and Emmerson Fittipaldi (67?) are the three oldest remaining F1 champions, and sadly with the passing of Jack Brabham, means there are no more drivers alive from the 1950s of F1, and only two remaining survivors from the 1960s.
As you say Col, it's a remarkable achievement given many didn't survive to finish their F1 careers in the 50s and 60s.
With Jackie Stewart came the push for better safety standards.
On another note, if you haven't seen both RUSH and the F1 documentary called "1", I totally recommend getting and watching both.
Likewise another brilliant documentary was Grand Prix: The Killer Years, in which Jackie Stewart talks of the crash in 1966 that lead him to push for safety reforms.
He is largely the reason why many survive today in the sport.