There's no hard age gate on the YouTube app itself. The restriction comes entirely from the Xbox Live / Microsoft Account used to sign in.
| Age | Account Type | YouTube Access |
|---|---|---|
| Under 13 (US) / Under 16 (EU) | Child Account (Family Group) | Allowed if parent enables "YouTube" in Content Filters. Restricted Mode ON by default. No live chat. |
| 13–17 (US) / 16–17 (EU) | Teen Account | Full YouTube access. Restricted Mode optional. Parent can still manage. |
| 18+ | Adult Account | Full access, no restrictions. |
Bottom Line: Any age can watch YouTube on Xbox if the parent configures the Microsoft Family account correctly. The app itself has no hard age gate.