Go to:
http://1914-1918.invisionzone.com/forums/index.php?
You don’t need to join to read. (it’s surprising how many Flypast Forum members turn up there!)
and search for “Harry (or Henry) Allingham”. Once agin this year, aged 109, I beleive he went to St Omer to lay a wreath.
I believe there may be an RFC mechanic as well, as I think Harry was RNAS, but you may need to inventive in your searching. Veteran or survivor in the relevant sub-forum may work, but you’ll probably get a lot of other stuff too!
Good luck!
Adrian