My title question is exactly my question : is it possible to create a freebsd 10 or 11 jail into a freebsd 9 instance?
The jail and the host system will both share the same kernel. So:
- Old jail, recent host: Running an outdated jail on a newer host should not cause any issue (the FreeBSD kernel will ensure retro-compatibility, enabled by default even for pre-FreeBSD 8 kernel as a kernel compilation option),
- Recent jail, old host: I would not try to run a newer jail on an older host. This would mean running a FreeBSD 10/11 environment using a FreeBSD 9 kernel which is definitively not recommended.
So, in your case, the answer is no, it is not possible (even if it may install successfully it will most likely lead you directly to a wall).