I'd say the 14 year old knows but just tries to milk it for extra presents!
When I was at Primary School (OK OK we called it Prep) Richard Dutton told everyone that Father Christmas was not real and it was really your Mum and Dad
I think in was in about 4th or 5th year
I was rather sceptical - but then I was cynical even at that age
but the concept did sort of make sense
so - naturally - I asked my Mum and Dad
I think they said something along the lines of
Well - if you say you believe then the presents keep coming - whether they come from Father Christmas or Mum and Dad
but if you start saying you do not believe and he is not real then if he is real then the presents might stop - now maybe Mum and Dad would make up the difference but is it worth the risk???
So - lets see what you think closer to Christmas??
It was never mentioned again and I still got a sack from Santa when I was in my 30s - although the quantity had dropped of dramatically since I was a kid!!!
(p.s.when I was much older my Dad said that if he was real then he wanted a serious word with him about the Baffle Ball he got me one year as it kept him awake half the bloomin' night after I found it!!!!)
I still believe Santa comes once a year
I don't recall ever believing in anything I couldn't sense or understand.
As a child I was quite content with my Mum and Dad.
We didn't ever promote false beliefs to our children, nor did we feel the need to disillusion them.