Who exactly is a virtuous agent? I know a virtuous agent, at least in Aristole's view, is one that acts accordance with reason. But is this agent myself or someone I know or someone I look up to or random or anyone?
It's anyone with the capacity to use reason to decide what to do, who decides well, and then develops good habits by repeatedly doing the right thing. ("Agent" just means someone/something who is capable of doing things. It comes from the Latin word for "doing.") Such people can use reason to act in one way or another, and thereby acquire the habit of doing things that cause them to be happy and flourishing (virtues), or the things that cause them not to be, which are vices. So to actually be virtuous such a person needs to use his or her reason and will to choose the right things to do, and thereby develop the habit of doing those things.