Ask someone to start from scratch in ATC at 40 years old and a very high proportion would struggle.
As someone who started with NATS as an assistant aged 42 I would have a very large wager that none of them would validate at LACC or LTCC within an acceptable time span..........
if at all !! 
It would be madness both practically and commercially to even consider them for training. You just don't take things on board as quickly and as thoroughly as you used to. (I used to think that was rubbish.......unfortunately you find out it's not).
Same applies when teaching people over the age of 40 to fly. They take considerably longer to train and if it wasn't for the fact that they
ARE PAYING FOR THEIR TRAINING most of them would be "chopped". There are always a few exceptions of course, but they are very few and far between.
However there is some good news though, that being under the new legislation you are no longer able to call me an
"Old Tosser".......... the use of the word "Old" is no longer acceptable
Regards
FBW