Legislation defines the end of minority status in England as 18 years old, Family Law Reform Act 1969 s 1, at 18 years. (A reduction from 21)
Genetics, personality characteristics, lifestyle & career choices, economic status, & luck are just some of the factors which determine when (if at all) individuals encounter the disadvantages of age - real (reduced mobility, impaired capacity, fraility, etc) or perceived (ageism).
NatCen's ELSA (see below) looks at the experience of those 50 years and older.
International bodies such as the UN & WHO make the qualification for older as 60 years and over.
The Law Bod's collection is spread over four, open access floors. So please always feel free to ask staff for directions when SOLO gives you some shelf marks/locations which are new to you.
On Level 2 (entrance level) you will find monographs dealing with the laws in UK & NI jurisdictions, Australia (A8), Canada (C1), NZ(N4) and USA(U4) at
KN150 - Person and Social Law
KN151.6 - Older people specifically
KN191.2 - Discrimination in Employment Law
KZ1 is where you will find Halsbury's Laws of England services in print.