"Tini is twenty years old."
Translation:Umur Tini dua puluh tahun.
I think it comes from satu which is one in indonesian, but I am not sure because Indonesian is not my native language
You use "usia" like a verb, when "usia" is a noun. (usia = umur), meaning "the age".
If you use a verb, the word order is correct: Tini berusia... Tini is aged of... (berusia/berurmu = verb, to be aged of).
If you use a noun, your word order is incorrect. The possessor has to be after the noun. So usia = noun, and Tini = possessor. You would have Usia Tini = Tini's age. Same order than anak saya = my child.
Tini berusia dua puluh tahun = correct.
Usia Tini dua puluh tahun = correct.
The "to be" verb does exist, and there are even several ways to express "to be" in Indonesian, depending on the context (identity: adalah, place: ada, color: berwarna, age: berumur/berasia), but Indonesian is a language where you don't repeat that is already mentioned elsewhere or obvious by the context.
The to be verb is optional, so when you say "Saya anak", (I child), we know that the "to be" verb is implied, and it's I am a child.
The longer version is Saya adalah anak (adalah = to be), but the common way is to simply skip this verb.