and giving more weight to old links and old sites... many sites do not last more than ten months
I hope you are right about the first part of that quote ~ it only makes sense that older sites in many (if not most) cases will have a degree of authority simply by virtue of their continuation. The logic being that if a site is still available, with reasonable updating, after 4 or 5 years, then it must have something going for it.
Re the 10 month expiration, that seems too short IMO. People buy domains for a year, and most hosting is annual, so it seems reasonable that a more accurate figure would be in the 24 month range. The thought being, they go online, give it a year, it's not working so they try one more year, it's still not working so they pull the plug. I have not much evidence for that, but I will say this: One of my sites is an arts directory that had over 3000 listings. I spent the last 5 days checking for deadlinks and found 500. I hadn't had the opportunity to do a thorough check for some time due to other issues, but even so, it was clear to me that a bunch of people are giving up on the internet as an income stream.