The Home Office has already carried out testing on images of people across different ethnicities and genders, including those that make up the asylum-seeking population, already in its operational system.
But test results have not been used for live decisions yet.
The technology is expected to be trialled for the first time on live cases of asylum seekers at Western Jet Foil, a processing centre in Dover, next year.
Age assessments of asylum seekers are already carried out by border force officials who use methods such as examining documents, appearance and demeanour to make an initial decision on age.
The new facial estimation technology will act as an additional tool to support officers at the border when a person's age is in doubt.
Social workers undertake assessments on asylum seekers claiming to be children, when their age is disputed by border officials.
The British Association of Social Workers (BASW) is warning that the government's plan to use AI in the assessment process will lead to major safeguarding mistakes.
"Assessing the ages of migrants is a complex process which social workers are best placed to do," said Professor Sam Baron, interim CEO of BASW.
"This important task should not be open to shortcuts through artificial intelligence, especially as the pitfalls of getting it wrong can lead to major safeguarding risks."
Last year, the UK government said it had concluded that the technology was the most "cost-effective option" to assess the age of asylum seekers.
But human rights groups have criticised the Home Office's plans to use the technology on children.
Anna Bacciarelli, a senior AI researcher at campaign group Human Rights Watch, said: "The government needs to scrap this deeply flawed approach to assessing child refugees.
"Experimenting with unproven technology to determine whether or not a child should be granted protections they desperately need and are legally entitled to is cruel and unconscionable.
"In addition to subjecting vulnerable children and young people to a dehumanising process that undermines their human rights, we don't actually know if facial age estimation works."
She said the technology had been used so far in shops and bars but not refugee processing centres, adding there was "no ethical way to move forward with these plans".
Correction: An earlier version of this story said age verification is carried out by trained immigration enforcement officers using X‑rays and MRI scans. The Home Office says it has the power to use these methods but does not currently do so.