The problem with climbing up is that you need to be extremely fit and an experienced Hiker, and if you're not, you'll gas out pretty easy. I'm in my early 30, and mostly I prefer going down, and you're right, probably that's because I have the knees for it .
Going down for 30 minutes or so is not too hard, it is when that 30 turns into 2 or more hours and the knees start to feel like jello lol.