The British Army should stop recruiting under 18-year-olds, campaigners and religious figures have urged.
An open letter from human rights group Child Soldiers International called on the Ministry of Defence to raise the joining age from the current 16.
All Church in Wales bishops signed the letter, along with other Christian peace groups from around the UK.
The MoD said it had no plans to change the recruitment age, arguing enlisting could be beneficial for youngsters.
At present, 16-year-olds can join the Army with parental consent and can apply from 15 and 7 months.
"We commend the MoD for having ceased routinely deploying children into conflict, but challenge its failure to stop recruiting them," the letter said.
'Double the risk'
It was signed by the Archbishop of Wales Dr Barry Morgan, the Reverend Sally Foster-Fulton, convenor of the Church and Society Council of the Church of Scotland, and peace groups run by Baptists, Methodists, Roman Catholics and Quakers.
The campaigners pointed out that in World War One, the youngest that recruits could join up was officially 18 - and that only those older than 19 were supposed to be sent to fight, "although it was known that many younger boys slipped through".
Dave, who joined the army at 16, told the BBC he thought recruits should be "at least 20".
"You've got two years training before you go into a theatre of war," he said. "But still, you're still a child.
"At 18 you're going through massive life changes and still experiencing."
He added that joining at the age of at least 20 would ensure "you've had a little bit of life experience".
Peter Felstead, the editor of Jane's Defence Weekly - a magazine reporting on the military - said the UK was out of sync with other European nations.
"It is an amazing opportunity to join the British Army for a lot of these guys who, otherwise, simply would not have that kind of opportunity to learn a trade, see the world and really make something of their lives," he said.
"But if you do look at the rest of Western Europe, 16 probably does seem slightly early. The average is more like 17 or 18 to join the armed forces."
An analysis of MoD figures by Child Soldiers International suggested 880 16-year-olds enlisted last year - 40% fewer than the year before and down from 3,600 a decade ago.
The group also claimed that of all the 16-year-olds recruited by the Army last year, nearly half (410) dropped out during training - although the MoD said "only a proportion" would have joined and dropped out in the same year.
The charity's director Richard Clarke said: "It's time for the MoD to recognise what more and more young people and their parents are realising - that enlisting at 16 is not in their best interests.
"Army training does not give young people what they need to succeed in today's economy, especially in terms of qualifications."
But that claim was directly contradicted by the MoD, which said the letter "ignores the benefits and opportunities that a military career offers young people.
"It provides them challenging and constructive education, training and employment, equipping them with valuable and transferable skills for life," a spokesman said.
"There are currently no plans to revisit the government's recruitment policy for under-18s which is fully compliant with the United Nations Convention on the Rights of the Child."
The UK is among fewer than 20 countries which have a minimum voluntary recruitment age of 16.