People aged 16 to 19 (or aged 16 to 24 if in continuous education or training since before age 20) can claim Incapacity Benefit after 28 weeks' illness or disability without needing National Insurance contributions.
In some circumstances, a claim may be made from the 16th birthday if that person was sick or disabled for the previous 28 weeks. Entitlement continues beyond age 20 (or 25) if medical conditions continue to be met.
Further information on Incapacity Benefit (Youth) is available from the Jobcentre Plus website.