We dont know EXACTLY how old Omega is, yet.
From How old is Omega in The Bad Batch? She’s not the youngest clone
At the end of season 1, we also learned the truth about Omega’s age. Though the Bad Batch appear to be adults and Omega presents as a child, their ages aren’t so conventional.
The Bad Batch: How old is Omega?
While we don’t know Omega’s exact age in numbers yet, it was implied in episode 15 — and confirmed in episode 16 — that she is older than the other members of the Bad Batch. She was already old enough to remember them being experimented on in Nala Se’s private lab before leaving her alone again.
Like Boba Fett, Omega does not appear to age at an accelerated rate as other Kamino-born clones do. So even though Hunter and the rest of her brothers are technically older because they age faster, at the time of The Bad Batch, she has been alive longer in standard years.
Unfortunately, since we don’t know when she was created, there’s no telling exactly how old she is. Though, from her appearance and normal aging, she should be about the age of a typical adolescent child, just still comparatively older than the Bad Batch.
We will likely learn more about Omega’s origins and former life on Kamino in season 2 as she comes to terms with losing the only place she ever called home.