No, 30 is not the new 90, or even the new 40, but it may be the new Pussy. At least in your neighborhood. There are no mile markers, only general trends. You know the fish diagram (PPST pg. 17)? The asymptotic line that represents training progression serves as a good model for lots of trends through time, and the effects of age are one of them. As you get older, the effectiveness of your response to training, your ability to recover, your ability to tolerate stress in general and unaccustomed stress in particular, your ability to train on little rest or bad diet, the perception of the pain and significance of injury, your willingness to push through a rep you may hurt yourself doing, and 80 other things fall off like that curve describes. It is a highly individual variation, but it will always conform to that curve in a general way. So, according to the curve, the gap between 15 and 30 is waaaaaay less significant than the gap between 30 and 45. Just think what it's like to be in the middle of the next one.