Lore wise, spirits, ghosts and demons have powers of ownership & possession – and this translates readily into game mechanics. In fiction-fantasy: ghosts, spirits and demons take over various things from cars, to people or even entire houses. In literature, plays and shows spirits can habituate wherever they please.
In 5e, Ghosts have this mechanic for humanoids. It is not clear if 5e also has ghosts of other sentient creatures such as dragons, giants or fae – if so, they would logically possess their own types. We are aware that this mechanic works specifically for goblins, with the nilbog. In many editions, clay golems seem to suffer from possession from 'evil spirits' as well.
In the demon-description blocks (MM) these creatures can possess objects via a specific summoning and enchantment. Demons then possess sentient beings by transferring out of these object-devices – though the mechanics for these steps is not clear, listed &/or obvious.
Main concern: given a mature 120+ day Clone, what allows any soul, spirit, demon or sentience to take over? Why would this inert body key ONLY to the original humanoid soul-spirit? Consider that demons are far more adept at taking over inanimate or 'inert' objects than any soul-spirit would be, original owner or not.
Assuming that this 120 day+ Clone could be taken over by another sentience, where or when does this end? If this invasive spirit or demon takes over, do they stay until natural death of the target body? Would a Ring of Mind Shielding or a sentient magic item qualify as allowable body-snatchers? Are there any RAW or RAI rulings that aught to be considered?
In Short How do ghosts &/or any alien spirit interface with a mature 120 day+ clone body? It seems odd and unfair that ONLY the original spirit-soul of origin has the 'keys' to this inert body.
Imagine the D&D version of Altered Carbon – it would be fun, interesting and at least as enjoyable as the Netflix series.
Best Answer
Yes, if the ghost can disturb the clone's vessel he can even use the body
If your ghost can see a clone in a crystal vat, it can possess it. Nothing in the clone spell states it cannot.
The contentious part is whether the clone can "wake up" inside the vat.
The clone spell states that a resulting duplicate
While inside its own vessel the clone is inert and essentialy in a state of suspended animation.
Once taken out prematurely the clone is no longer enduring indefinitely and (fully) inert.
And from here it goes into interpretation territory.
Without a mind or soul the newborn clone is nothing but a ragdoll. Physiologically, since the clone's body is "fully developed" its autonomic nervous system (responsible for keeping your heart beating, your breathing steady, etc.) should at least allow it to slowly starve to death. A ghost could reasonably possess and use this body like that of a normal living person.
A little disclaimer:
The spell doesn't mention anything about a prematurely born clone breaking the bond between it and its original. Imagine the suprise of the original when its soul slingshots into the clone's body in the middle of his own wedding, or whatever the ghost is up to using this body.