They don't stay a baby for very long at all. I'm not sure how big a hatchling is, but by 6-8 weeks old a dragon should be 6 inches long and they'll grow constantly through the first year of life until they hit their adult length of 16-24 inches long (depending on genetics, husbandry practices, etc.) A dragon does most of its growing in the first 12 months and is a full adult at 18 months old.