
IF played correctly, with caution, with humility, and with a good story and purpose for your character, this is a completely possible character in my opinion. I think you are going to get more people who will probably just say don't bother because of the risks, but honestly, it is no fun to always just have a safe character, and if you do this right, I think it is just enough on the side of unimportant that it could work quite easily.
Some things to consider:
The poster above is right, and I think that you answered this pretty well, clones don't necessarily know everything there is to know, and possibly could be taught or programmed with the exact amount of knowledge they need. Another possible approach to this is making your character have some memory loss. If you can RP with friends who are willing to accept your character for what he/she is, and who can help you make it convincing that maybe your character senses something is not right, something is a little off about themselves, and have some memories that over time come back (which will allow you to retain some of the Allaghan societal queues, but not have to deal with tons of lore to learn/make up which I wouldn't ever recommend). This kind of thing can also be justified with the long expanse of time since their creation, maybe after being dormant for so long, they have forgotten their purpose? If you don't like these, or don't have the RP friends to support these, feel free to do whatever you want, I just thought these were some decent plot ideas?
One last thing, I think a great idea to really emphasize on a character like this is: the future! A clone who has lost purpose (and possibly memory), and is living in a time with which they are not familiar, has a great potential to be a wanderer or searcher, going along an unseen path and trying to find a new goal in their lives, which in any kind of character can be a real treasure to RP with some hard work and creativity!
Above all, and this has been mentioned above in a way, play with humility! Do not be: "I am an Allaghan clone guys! Look at me! I am thousands of years old!" be more: "Hello my name is Doga/Unei...made up last name, no real family, unknowing of cultural cues or the simple world of today's Eorzea, but still a person with all the emotions and thoughts a normal person has, nice to meet you, lets grow together (as I figure out my place and self)!" because that is the way that you are going to get what you want and still enjoy all the many wonders of RP in our big talented and creative community!
Okay, enough rambling, hope this helps, and good luck! Momo would be happy to work with you at some point if you are on Balmung!
Some things to consider:
The poster above is right, and I think that you answered this pretty well, clones don't necessarily know everything there is to know, and possibly could be taught or programmed with the exact amount of knowledge they need. Another possible approach to this is making your character have some memory loss. If you can RP with friends who are willing to accept your character for what he/she is, and who can help you make it convincing that maybe your character senses something is not right, something is a little off about themselves, and have some memories that over time come back (which will allow you to retain some of the Allaghan societal queues, but not have to deal with tons of lore to learn/make up which I wouldn't ever recommend). This kind of thing can also be justified with the long expanse of time since their creation, maybe after being dormant for so long, they have forgotten their purpose? If you don't like these, or don't have the RP friends to support these, feel free to do whatever you want, I just thought these were some decent plot ideas?
One last thing, I think a great idea to really emphasize on a character like this is: the future! A clone who has lost purpose (and possibly memory), and is living in a time with which they are not familiar, has a great potential to be a wanderer or searcher, going along an unseen path and trying to find a new goal in their lives, which in any kind of character can be a real treasure to RP with some hard work and creativity!
Above all, and this has been mentioned above in a way, play with humility! Do not be: "I am an Allaghan clone guys! Look at me! I am thousands of years old!" be more: "Hello my name is Doga/Unei...made up last name, no real family, unknowing of cultural cues or the simple world of today's Eorzea, but still a person with all the emotions and thoughts a normal person has, nice to meet you, lets grow together (as I figure out my place and self)!" because that is the way that you are going to get what you want and still enjoy all the many wonders of RP in our big talented and creative community!
Okay, enough rambling, hope this helps, and good luck! Momo would be happy to work with you at some point if you are on Balmung!