NMcM v SSWP (DLA)  UKUT 312 (AAC),  MHLO 88
"What is meant by the statutory expression 'a state of arrested development or incomplete physical development of the brain'? This is one, but only one, of a number of tightly defined conditions which must be satisfied under the 'severe mental impairment' rules in order to qualify for the higher rate of the mobility component of disability living allowance. It is the main issue arising on this appeal. Social Security Commissioner’s decision R(DLA) 2/96 has long been recognised as authority for the proposition that the human brain is fully developed before an adult reaches the age of 30. On that basis it has been consistently held that a person who suffers from what would otherwise be regarded as 'a state of arrested development or incomplete physical development of the brain' does not qualify under the SMI rules if that condition first occurs after the age of 30 (e.g. as a result of traumatic brain injury). I refer to this as the 'age 30 cut-off rule'. In the light of the expert evidence reviewed in this decision, I decide that the age 30 cut-off rule is no longer good law and R(DLA) 2/96 should no longer be followed in that respect."