I can’t find an answer for this. Is a newly emerged queen hairier than a two year old one? Are there any other characteristics to watch out for to distinguish between a new mated queen and an old one.
Yes, as they age their hairs are gradually rubbed off. You still can see older queens that are relatively hairy though, it should not be used as a definitive guide to age.
Other things to look for are often a judgement call and learned by experience. Older queens darken a bit, but again since color can vary with breed this is a hard one for newish beekeepers, experienced beekeepers can probably judge it though.
Older queens can look "doddery" in comparison to young queens, young queens move faster and just generally look more vigorous.
However most of these things are a judgement call rather than an exact science, but most experienced beekeepers can put all the factors together and come out with a reasonably accurate estimate of age for the queen.
Also, are all virgin queens small or can they look just like older queens too?
Immediately after they emerge from the queen cell they can be quite big, then they take a few poops and get smaller. They then get pretty small in preparation for their mating flight, and in that state can also move very fast and are very energetic. After the mating flight they swell up again.