phrone,
Age is not really an acceptable excuse. If you truely are younger and care about your reputation, then your response to posts like mine above would have not have been, "that is nonsense", but rather, "cool, thanks for the advice... I learned a lot from this and will do things different next time... and find out how to do backups". I would think you would work something out that is fair with the buyer. Your attitude is that this is not your fault, or your problem.
I don't know the details, so I'm just posting based on what you and the buyer have said in public. You appear to have owned the site and sold it to him. You have admitted several times that you didn't take the proper precautions to secure the site, or back it up properly. What your partner did or didn't do is not relevant... since you have represented yourself as the owner... you were responsible. As a tip for the future, if you've never tested your backup, then you don't really have a backup. Whether he is complaining or not, I don't know... but I think that other people are interested in the outcome so they can determine whether they'd want to do business with you. Many dnforum members buy and sell sites on a regular basis, and track record is extremely important.
Your age has nothing to do with this. Either you deal with this the right way, or you don't. A 15 year old could do the right thing, and a 40 year old could do the wrong thing and cheat someone... we are talking about integrity, not age. I expect that there are many younger dnforum members that would be offended that you would use age as an excuse... because it then stereotypically affects their credibility in a negative way.