User-generated content and meta programming

I was metaphorically throwing a ball against a wall today, thinking about how tedious it is to come up with all the items and characters in an RPG. So, I want to make system where people can create items to appear in games. As far as I'm concerned, an item is primarily a list of stats, although it should probably have a graphical representation and a description. The items have to conform to specifications on which stats they have and what range of values a stat can have. For example, a sword must have an attack value between 0 and 99. The items may combine in ceratain ways to create more powerful items. The more I thought about it, the more parallels I could draw to object-oriented programming. People are essentially writing classes for game items. I am interested in implementing at least a demo of this system. Sure, I could slog through it step by step, but it seems that I'd be rewriting major parts of the language. Could there be a way to avoid this?