At face value, it seems like a deal to me, if the glass is pretty. Although I can recognize the bargain price, I'm still stuck by Petco's $1/gal promotion that they do once or twice a year, so the condition of the glass really is my deciding factor in a used aquarium.
My first thought about age are:
1) Things today aren't made like they were, so I'm hesitant of newer tanks more than 5-7yrs old, given that I would like to get another 5-10yrs out of it.
2) On the same note, something of the age you are considering that has been maintained and in regular use is probably still of high quality.