The child was one of 75 referred from Wales due to their gender confusion - almost double the previous year.
Seven years ago there was just one Welsh referral through the National Health Service, the BBC reported.
The figures are from the Tavistock clinic - the only centre offering gender identity treatment to young people in England and Wales - which have seen a sharp rise in recent years.
About 2,000 children and young people were referred there through the NHS last year - an increase of 42 per cent on 2015/16. The increase in referrals from Wales was 79 per cent.
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Jamie Pallas from Gendered Intelligence, which works with transgender children and young people, said: "In general, there has been a great increase in awareness, so if young people are talking to their parents and have questions generally, their parents may be more aware in what they can do to help them. People know they can approach their General Practitioners and ask for referrals.
"There is also a lot of information available on the internet and I think that has helped young people. Also, we are seeing schools support young people."
"There is also greater knowledge about specialist gender clinics and the pathways into them, and an increased awareness of the possibilities around physical treatments for younger adolescents. The long-term health and psycho-social wellbeing of young people is always our priority," Dr Carmichael said.
Kate Hutchinson, director of Wipe Out Transphobia, said there was no visibility, "no-one to talk to", and no trans youth organisations when she was a teenager in the 1980s.