Many social landlords refuse to let to 16 and 17 year olds , either because they are concerned that minors cannot hold a tenancy, or they are concerned that they cannot be held liable for rent.
A 16 or 17 year old cannot hold a legal interest in land. In legal terms, if they sign a tenancy agreement they will hold a tenancy ‘in equity’ whilst the landlord holds the legal tenancy on trust for the young person until they reach the age of 18. This means that the landlord cannot take possession action against the young person because they would effectively be taking action against themselves. The young person will however be bound by the terms of the contract, and liable for rent payable under it. A 16 or 17 year old can hold a licence.
For more information, see Shelter Legal - Tenancies for minors