As Lord Soley mentions, William Pitt the Younger became Prime Minister at the age of 24. He was elected as an MP at the age of 21 and became Chancellor of the Exchequer eighteen months later. He then twice refused the premiership before accepting it in December 1783. The Tory preponderance in the Lords that existed until 1999 is largely attributable to the many peerages created during his period of office.

Pitt was not unusual, at least not in terms of parliamentary service. If anything, it was surprising that he was not elected until he was 21. Before the passage of the Parliamentary Elections Act of 1695, ‘infants’ (those who had not reached the age of 21) were disqualified from sitting in the Commons by the law of Parliament (according to Sir Edward Coke), though that did not stop some under-age Members being returned. Some of those who sat in Charles II’s Pensioner Parliament, for example, were reported to be 14 or 15 years of age. The 1695 Act placed a statutory bar on membership of those who were not yet 21. Despite this, in the period from 1734 to 1832, 81 MPs were elected who were under age, all bar one being allowed to take their seats. A notable figure among the 81 was Charles James Fox, who made his name as an outstanding debater while still formally under-age.

However, the law was enforced following the 1832 Reform Act and no one since that time has been returned to the Commons under the age of 21. Some MPs have been returned at the age of 21 (the most notable recent example being Bernadette Devlin in 1969) and under the Electoral Administration Act 2006, the qualifying age for candidature has been lowered from 21 years to 18 years – so far resulting in some councillors being elected under the age of 21, though as yet no MPs. It is presumably only a matter of time…

I was one of those who pressed for the qualifying age for candidature to be lowered. (I published an article on the subject in Public Law in 1980.) For me, the essential principle involved is one of voter choice. I think electors should be free to elect whoever they wish as their representatives. It is not for others to limit their choice.