"He is older than her."
Translation:Il est plus vieux qu'elle.
"vieux" is both singular and plural. However its feminine counterpart "vieille" has a plural form: "vieilles".
Note that "older than her" is incorrect English. This is a very common error, but, nonetheless, an error. The complete sentence is "He is older than she is."
"vieil" is used before a vowel or a mute "h".
- un vieil animal
- un vieux lion
Most of the time we don't use "ancien" (as an adjective) for people, at least not for the meaning "old" (age).
We can use it however to mean "old" (ex-) for someone who lost his position (or anything like that):
- l'ancien entraîneur de l'équipe
We can also use it to mean "old" (age) as a noun:
- les anciens de ce village
I put "Il a plus age qu'elle", but it turns out it should have been "il est plus age qu'elle". But in French you don't say, I AM 20 year old, you say I HAVE 20 years. So why is it he IS more old than her, rather than he HAS more age than her?
Because adjectives are used with what we call in French "un verbe d'état" (a stative verb).
Here are all the stative verbs in French :
"être, devenir, paraître, sembler, demeurer, rester, avoir l'air, passer pour"
When adjectives are used with such verbs they're called "adjectif attribut".
Of course they can be used without a verb as well, then they're either "adjectif épithète" (not separated from the noun) or "adjectif apposé" (separated from the noun by a comma).
Watch out because it seems that English names for these categories are misleading. For example it seems that "adjectif épithète" is called "attributive adjective" in English.
Because the exercise uses feminine for the object, and masculine for the subject.
Can we use the "avoir plus de l'âge" or something of the similar construction here?
"avoir plus de l'âge" isn't correct French. You can use either "être plus vieux que" or "être plus âgé que".