Before reading this, you should take at least a passing glance at my main fantasy hockey article since many of the factors which apply to a forward’s fantasy ranking also apply to defencemen. However, more than anything, you can uncover a defenceman’s fantasy value by how much powerplay time they get. I outlined that in the category PP Rk. #1 means they’re always on the first powerplay unit; #1a means they may be on the #1 unit, but could also be on the second unit. (#2 of course means they’re on the 2nd unit).
As far as age goes, a defenceman’s prime is generally slightly later than a forward’s. There are a few young elite players like Doughty, Myers, Karlsson, and Subban, but for the most part great defencemen are 25+. And if a player doesn’t experience too many injuries, they can be productive well into their 30’s. Generally only the finesse defencemen age well though – like Lidstrom, Boyle, and Visnovsky. More physical defencemen like Pronger and Chara don’t tend to age as well.