Is "Umur" needed or can you omit it?
You can omit it.
The sentence will still have the same meaning.
Different structure, same meaning, something like this
"Umur kamu sepuluh tahun." = Your age is ten years.
"Kamu sepuluh tahun." = You are ten years.
Yes it sounds weird haha
But if you add "-nya" at the end of umur, that will be natural and informal
"Kamu sepuluh tahun umurnya"
I feel like "You are 10" should be accepted. You'd never say "Your age is 10" in English.