Wing Commander harry Day was a WW1 vet who flew and was shot down in early October, 1939. He was effectively SBO for all British Air Force POW's the first two years or so in the bag and set the standards for general British POW conduct during that time, basing it all on the Kings Regulations and his own common sense. He was just shy of 41 at the time he was shot down.
Another oldster was F/L Bernard 'Pop' Green, who roomed with Wings day at Stalag Luft III. Another WW1 vet, he was 53 when he lied and pulled enough strings to get himself a position behind a gun on a bomber in 1940. He was one of the lucky escapers on the Great Escape that didn't get shot.
G/C Herbert Massey was another 41 year old POW. He took over the title of SBO at Stalag Luft III from Wings Day, but remained in the background, sparring with the German, while Day handled the day to day camp operations.
If I'm not mistaken Freddie West did some flying during WW2 with the RAF as well. He was another WW1/RFC vet who had lost a leg in that war.
As an aside, Major John Dodge, who was army, managed to stay with Air Force POW's throughout the war. He was 52 when captured (if memory serves) and was a WW1 vet as well.
Lots of the old guys there!