No, one can't confirm age by carbon dating. That doesn't mean we can't make a decent guess by other methods.
There is an interesting case of a 33 year old Texas woman who enrolled in 10th grade in Texas. She said she had no transcripts because she had been homeschooled. She looked like a teenager and acted like a one too. She even fooled her new 23 year old boyfriend. So it happens. It also happened in the Little Leagues World Series, if I remember correctly. A twenty-something guy passed himself off as a 14 year old. He was a star (for a while).
In children and adolescents, the combination of a dental exam, dental films and bone X-rays can narrow a one's biological age well. Once the bones are done growing in length, that avenue is closed.
After that, someone might have to provide a tooth. Chemical analysis of tooth dentin, such as aspartic acid racemization, has shown reproducible and fairly precise results.
Global levels of carbon-14 (14C) have been carefully recorded over time. In one 2010 study, forty-four teeth from 41 individuals (one per individual) were analyzed
using aspartic acid racemization analysis of tooth crown dentin or radiocarbon analysis of enamel. Teeth from individuals with dates of birth ranging from 1936 through 1994 (aged 13–70 years) were analyzed, and where the date of birth was known, yielded a 14C-based date of birth estimation accuracy of 1.3 years (S.D. = 0.9 years). In one case, a date of birth was determined to be 1948.4. In another, it was determined to be 1988.
[T]en of these were split and subjected to both radiocarbon and racemization analysis. Combined analysis showed that the two methods correlated well (R2 = 0.66, p < 0.05). Radiocarbon analysis showed an excellent precision with an overall absolute error of 1.0 ± 0.6 years. Aspartic acid racemization also showed a good precision with an overall absolute error of 5.4 ± 4.2 years. Whereas radiocarbon analysis gives an estimated year of birth, racemization analysis indicates the chronological age of the individual at the time of (tooth extraction).
During the course of aging, l-forms of amino acids are transformed by racemization to the d-forms.
[T]he extent of racemization of amino acids may be used to estimate the age of various tissues. Of all stable amino acids, aspartic acid has one of the fastest racemization rates and is therefore the amino acid most commonly used for age estimation....[T]eeth are the tissue of choice for age estimation analysis.
Both methods have strengths and limitations.
The radiocarbon birth dating method can tell the birth date of the person regardless of the time of (extraction). However, the time window for this analysis is limited to subjects born after the early 1940s because the calculations are based on the measurement of bomb pulse-derived 14C.
Clearly this wouldn't be of too much use in people trying to pass themselves off as teens.
Some studies of aspartic acid racemization report accuracies of age ±3 years. The radiocarbon and racemization can further narrow it down.
Why did Charity Johnson pretend to be a teenager for 20 years?
Age Estimation in Forensic Sciences APPLICATION OF COMBINED ASPARTIC ACID RACEMIZATION AND RADIOCARBON ANALYSIS
Strategy for the estimation of chronological age using the aspartic acid racemization method with special reference to coefficient of correlation between D/L ratios and ages