Use 'aged' to state ages clearly (for example, aged 17 years or aged 19 to 30 years) and avoid hyphens unless needed for clarity - for example, write '15 students aged 16' or 'aged 4 to 16 years', not '16-year-old' or '4-16 years'.
Avoid vague terms like 'over 50s' or 'under‑18s'; instead specify the range (for example, 'aged 50 years and over'), using alternatives such as 'before the age of' or 'after... years of age' where 'aged' is not suitable.