Attempts to double the age of criminality in Scotland to 16 have been blocked by MSPs.
Liberal Democrat Alex Cole-Hamilton proposed amendments to a planned new law to increase the age from eight to 12, arguing an additional increase would be “in line with international responsibilities”.
The current age is one of the lowest in the world, and below the rest of the UK at 10.
The age 12 recommendation was first mooted in 2015 but is only now being put before the Scottish parliament.
During a debate on the Age of Criminal Responsibility (Scotland) Bill at stage two at Holyrood’s Equalities and Human Rights Committee, Mr Cole-Hamilton said the United Nations will increase the baseline age from the current 12 to 14 in the coming days.
He said: “Unamended, this Bill is an embarrassment… I will only vote for this Bill because the current age of criminal responsibility in Scotland is, quite frankly, medieval.”
He said history, the international community and the children affected will judge the government for not backing the further increase, which he said wrecks any claim that Scotland is a human rights champion.
His amendments to raise the age of criminal responsibility to either 14 or 16, to give 18 months for this to come into effect once the legislation raising the age to 12 is passed, or to increase the age of criminal prosecution to either 14 or 16, were all voted down by five votes to two.
Mr Cole-Hamilton was backed by Labour’s Mary Fee in voting for the change, while SNP and Conservative committee members voted against it.
The Tories’ own amendment to give Scotland’s top prosecutor, the Lord Advocate, discretion to become involved in “exceptional cases” of children below 12 was also defeated by five votes to two.
The Lib Dem MSP said last year, 11 cases of offences being committed by 12 and 13-year-olds were taken to court. He argued this shot down the government’s case that a further increase from the age of 12 would cause a capacity issue.
He criticised the SNP for an argument he claimed suggests the children’s hearing system exempts Scotland from international standards, saying: “When it comes to the international minimum, we don’t get a pass.”
Minister for Children and Young People Maree Todd urged the committee not to back the amendments for a further age rise.
She said she had “significant concerns” about using the Bill to raise the age past 12, highlighting worries about the readiness to deal with further increases, which she said would require additional primary legislation.
She also raised capacity concerns, adding: “I think that by setting arbitrary time limits there is a risk we rush this and fail to address all the matters that need to be considered. We need to take the time to get it right.”
An advisory group set up by the Scottish Government in 2015 recommended that the age of criminal responsibility be raised to 12.
Last year, ministers held a consultation on the age change between March and June, but did not take a firm position on the proposal.
A report was published in November and the following month Early Years Minister Mark McDonald confirmed the case for change was "clear and compelling", with the consultation revealing "overwhelming support" for the move from police, victim support organisations and charities that help vulnerable children.
He said: "I acknowledge that some will be concerned at the change and its impact. What should reassure them is that children and young people want this, victims' groups want it, police and prosecutors want it, and the United Nations has called on us to do it.
"This reform signals our commitment to a smart, evidence-led and rights-proofed approach.”
Referencing the death of toddler James Bulger, murdered by two 10-year-old boys in Merseyside in 1993, Mr McDonald emphasised that while there has been no similar Scottish case, "sensible and proportionate" safeguards would be put in place to deal with the possibility of serious cases.