Well, close, she’s 36, but looking good for it. I know plenty of people in their thirties and even 40’s who just haven’t seemingly aged in decades. Sometimes it all catches up with someone at once… Sometimes it is being fortunate enough to have the money for treatments (Not plastic surgery, but being able to afford beauty treatments) I mean look at some celebrities. I would never have believed that Charlize Theron is less than a year younger than me being 45, considering how she looks, and Helena Bonham Carter is 54!
Some people just get lucky.
Well…I mean…They’re not. I mean quite famously not. I mean leaving aside the perpetual myths that Walt Disney was cryonically frozen (He was actually cremated) then Freezing temperatures can be widely seen in our own world to not -prolong- that youthful glow, but to kill it quicker. There is in fact no correlation between Freezing temperatures and prolonged life. In fact people who spend their time constantly in freezing environments tend to look -older- as their skin grows weathered and a bit wrinkly, especially around the eyes. Which makes sense, as they are the only part of our body that is exposed which is perpetually filmed with liquid.
Only in the sense that she has a fanbase as thirsty as Sylvanas fans, and Christie Golden has got her back, and she ain’t ever going to get killed on her Watch. She’s just a 36 year old chick who looks good for her age, and to be fair, we all know plenty of those in real life. Well, probably.
Well, I can’t remember with of Katherine’s children was born first, but it is entirely possible that with Jaina being 36 that Katherine is at youngest (assuming our real world sensibilities) 52 years old. Thats assuming Jaina was born when Katherine was 16, but I seem to remember that she was not the eldest Proudmoore child. Either way, This puts Katherine between 52 and 60-ish, and women are perfectly capable of looking good at that age, men too. Some people are like a fine wine, they improve with age. They do seem to have good genes though, which can’t hurt.
Mages -can- prolong life with magic, but not necessarily youth. These things tend to bite people on the backside if tried too much.
Thrall has the advantage of being (I’m pretty sure) younger than Jaina, though not by that much, he was a young teen at the time the Third War started, just one who was able to inspire a people and lead them (Forget Yrel, Thrall is Azeroth’s Jeanne D’arc 
) Sometimes people forget, because of their temperaments, that Garrosh was actually -older- than Thrall by a fair bit.
There is also the thing that it may just be the improvement of graphics. Jaina now, looks younger to my mind than she did in WotLK. Harder to say with Thrall, but he does seem a bit more ‘clean and less wrinkled’ than his old model. The only models that really seem to have been shown to have aged are obviously Anduin and Wrathion, and to an extent Lor’themar Theron, but thats more because they finally gave him his gnarly scars he had anyway since the game started.
Might just be that the graphics have improved…heh heh.