He was selected as consul ordinarius in his ninetieth year, serving with Gaius Antistius Vetus in AD 96.
Aged 45 or 46, Valens was already older than the average legatus commanding a legion in Roman Britain when the governor Publius Ostorius Scapula died.
[2] Although emperor Claudius quickly selected a replacement for Scapula, Aulus Didius Gallus, between Scapula's death and the arrival of a new governor the Silures had defeated the legion under Valens' command.
[3] The defeat in Britain likely set back his career, for Manlius Valens does not appear in the historical record until towards the end of the reign of Nero, when he became legate of the newly formed Legio I Italica at Lugdunum; this fact caused Birley to comment that "at sixty-two or sixty-three he is by far the oldest known legionary legate.
Why Domitian selected him, a general of an enemy of his father, as eponymous consul almost 30 years later, Birley confesses is a mystery.