looked after child ? claiming benefits

HI
I have a young man aged 16 who was previously living in a foyer project, claiming UC and HB (I assume on the grounds of estrangement). To my knowledge, he wasnt a looked after child at that point.

He is now accommodated under section 20 - which I think now makes him LAC.  The LA are meeting the cost of accommodation as they are required to do, but UC is still in payment. 
My question is that if this young person is looked after for at least 13 weeks, does this then make him an eligible child and therefore not able to continue UC claim and LA have a duty to maintain?

or does the fact that he is looked after after age of 16 make a difference? not sure whether UC should cease?  I have searched but I can only find that LA have a duty to accommodate but cant see anything relating to maintenance also. (just to add that he does have some health problems so may qualify for UC anyway if he has had a WCA) we are trying to ascertain what is included in his UC.

social worker has just come back to me and as this is section 20 and not 17, they will be paying an allowance (just in case anyone else has similar query) so they will now notify UC that he is a looked after YP.