Labour will introduce legislation to lower the minimum age for train drivers to 18 in the House of Commons this week, as figures show fewer than 3% of drivers on Great Britain’s railways are under 30.

The government is pressing ahead with its proposals for teenage recruits, lowering the minimum age from 20, in a move that ministers hope will stave off a potential shortage of thousands of drivers.

A looming mass exodus through retirement threatens to intensify driver shortages and worsen train reliability, with a lack of crew already a big cause of late-notice cancellations.

The current average age of Great Britain’s 24,000 train drivers is 48, and about 25% of them will reach retirement age before 2030.

According to a National Skills Academy for Rail report, that could mean a shortfall of 2,500 drivers in four years’ time.

While a number of train drivers continue to drive into their 70s, most retire well ahead of the state pension age as they become eligible for a railway pension at 62.

Almost two in five train drivers in Wales, which has the lowest life expectancy in Britain, are over 55.

The latest workforce survey, published in Department for Transport assessments last month, showed that fewer than 3% of train drivers in Great Britain are under 30 years old.

The train drivers’ union Aslef, which has long campaigned for the minimum age to be lowered, admits members up to the age of 35 in its youth wing. Aslef said bringing 18-year-old drivers into the cab would not only help the railway recruit the numbers it needs but also increase diversity and better reflect the communities it serves.

Rob Kitley, 31, the chair of Aslef’s young members committee and a driver with GWR, said it was “fantastic to see the legislation now being put in place”.

He said: “As young train drivers we have been campaigning for this change for many years, in order to level the playing field and bring our industry into line with other parts of public transport, such as buses and the London Underground.

“By widening the goalposts to allow younger candidates to join the driving grade, we open the door to new talent which may otherwise have been lost.”

The government declined to comment ahead of an expected announcement. However, discussing proposals last year, the transport secretary, Heidi Alexander, said they would help in “future-proofing our railways against delays and cancellations caused by a shortage of drivers”, and also drive growth by “getting young people into the workforce and putting them on track for a skilled and fulfilling career”.

The move to a nationalised and integrated Great British Railways may have eased the change, with train operators on limited franchises sometimes reluctant to invest in training younger drivers – regarded as more liable to change jobs than midlife joiners, often ex-service personnel.

Aslef has argued, however, that recruiting younger drivers will increase diversity, with more people joining straight from school.

Dave Calfe, the union’s general secretary, said: “At the moment, many young people make their career choice at 18 and the industry misses out. This change will widen the opportunity for the rail industry to recruit the large numbers of train drivers required over the next five years.”

Getting a job remains challenging, with competition for places, psychometric tests and 12 to 18 months of training. Average salaries are about £70,000.

Drivers are already able to start at 18 in other parts of Europe, including Germany, the Netherlands and France. Curiously, teenage train drivers may soon be allowed on either side of the Channel, but not to drive trains through the tunnel that connects them, because of a bilateral agreement between the UK and France.