Tutankhamun reigned for around 9 years, making him about 18 when he died.
How do we know when Tutankhamun died?
1) Forensic analysis of his mummy has put his age at death at about 18.
2) Clay seals on wine jars found in his tomb record not only the type of wine and the vineyard, but also the king's regnal year when each wine was laid down. The highest recorded date is Year 9, suggesting that Tutankhamun died in that year.