The AP Stylebook says to make reference of age when it is deemed relevant to the situation. If someone is quoted as saying, “I’m too old to go back to school,” the age is relevant. Generally, you should use ages in for profiles, obituaries, significant career milestones, and achievements unusual for the age.
Do not use ages for sources commenting or providing information in an official capacity. Appropriate background, such as “mother of two young children” or “a World War II veteran,” may suffice instead of the actual age.
AP Style holds that when referencing ages you should always use figures. For example,
- The worker is 30 years old.
- My brother is 25 years old.
- The building is 18 years old.
- The 50-year-old wine bottle is now ready to drink.
In those instances where “years” or “years old” are not required, the figure is presumed to be years.
Use hyphens for ages that are expressed as adjectives before a noun or as substitutes for a noun. For example,
- The 5-year-old boy went to school (adjective before a noun).
- Kindergarten is for 5-year-olds (substitute for a noun).
Some more examples,
- My sister, 30, is older than my brother, 28.
- The woman is in her 30s.
It is important to remember that, as in our last example above, there is no apostrophe between the figure “30” and the “s.” For example,
- I had the best time of my life in my 20s.