"Jaraĝa" is like the English "years old". "Jara" would be the adjective form of year, like "jara fino" would be the year end.
Sorry, I didn't notice the context. I should have looked above.
If you use a number-jara (separating the number and the "jara" with a hyphen, like in the example above, then it's usually assumed that it is referring to age, or something to do with that many years. Thus, you can probably figure it out by context.
That's one of the features of Esperanto. If your vocabulary is limited - for example, if you don't know the word "aĝa" - then you can sometimes still work around that by using the words you do know. You can use "kvin-jara" or "kvin-jaraĝa" whichever suits you. I probably use the longer version more, because it's more descriptive, and you definitely know you're talking about a person's AGE, and not something else. But if someone comes up to you and says, "Mi estas tridek-jara," you will know what they are talking about from context.
Hope this helps!
This lesson keeps marking me incorrect for forgetting hyphens and it's driving me crazy.
Is it just me or there is an underscore between the words "years" and "old" in the answer?