There were lots and lots of young men flying in Lancasters, but the oldest crew members (not very many) were usually gunners (and in their 40's).
To give context, the Lancaster was a horrible bomber to get out of. On average only one in 7 crew got out when it was shot down (8 crew in the Pathfinders-and extra navigator).
So with about 3400 lost and an average of 6 crew lost per loss, then you can see the Lancaster casualty rate would be very high.