A beginner 18-year old probably needs something fairly sturdy and simple. The more do-dads and zippers, the more to break. He probably would use it for more than just backpacking- road trips, perhaps take it on an airplane. 18-year olds are not know for being gentle on their gear! The more fragile UL equipment is outside your budget anyway. North Face gear is known to be sturdy but heavier than other brands.

Kids are different, but is he influenced by the "cool" factor? Maybe ask one of the younger REI employees what the young are now considering "cool". I am not one to be influenced by "cool" yet a GG pack I recently purchased (and returned due to other problems) was so ugly that I even choked on it.

If he is going to mainly do weekend or short trips, 40-50 L may be fine. If he wants to get into longer trips, I would go for 55-60 L. I agree that 18-year old guys do not need UL gear- and a 3-4 pound pack should be fine.

I too am still looking for a pack and there are a lot of good sales going on right now. Lots of close-outs of last year's models.