In the family of "John de Malpas, of Hampton and Bickerton, died before 8 Hen. V" is listed "Ellen, wife of Urian de Brereton, sole suriviving sister and heir, 11 Hen. VI. o. s. p. [died without issue].'
'... 11 June 20 Hen. VI. a mandate was issued to the escheator to prove the age of Ellen, then wife of Urian Brereton.'
On page 358, in indicating the death of her sister Katherine, the same date is given as June 20, 11 Hen. VI. Since Henry VI's reign started in August 1422 (Wikipedia), this date would have been June 20, 1433. I assume that "prove the age" means to prove that Ellen was "of age", that is, at least 21 years old.