We all think that Fernando Alonso is old with doing F1 race at his age of almost 42 years. Nevertheless, he is by far not the oldest. Lucky him!
Monegasque Louis Chiron, you probably never heard of him, was 55 years 292 days old when he was at the start of the Monaco Grand Prix in 1955. He broke the record of Frenchman Philippe Etancelin who was 55 years 191 days old when he started at the French Grand Prix in 1952. Belgian Arthur Legat started at the Belgian Grand Prix in 1953 when he was 54 years 22 days old.
All the oldest drivers in the top 10 entered Formula 1 in the 50's. It says something how the sport developed in the years after that. More professional and although an age does not say anything. Alonso is proving that!
There is a driver who was older than normal when he entered Formula 1. It was Damon Hill. In 1992 Damon Hill made his debut for the Brabham team at the age of 32 years. In 1993 he would get a seat at the Williams Team next to Alain Prost.