Chapter 20 lists him as 19, while FL is 14 and marriage can happen at 15. Older time setting, when people got married off young since people generally didn't live very long compared to now.
"From the Song to the Ching dynasties, the age of marriage was set at 16 for men and 14 for women." And life expectancy was 24 to 35, though some did live longer (like nowadays people living 100+ years).
That said, life expectancy in most novels isn't that extreme.
