Absolutely. If you ask for a piece of meat to be aged for you, you can (1) choose the specific cut to be aged (usually only whole parts can be aged because of the significant amount of moisture loss and amount of meat that has to be trimmed after aging), (2) the manner in which a piece of meat is aged (wet aged, wet aged and dry aged, or dry aged only), and (3) the length of time a piece of meat is aged.
I recall reading in a number of articles that 21 to 28 is generally considered best, with meat aged over 28 having a decidedly funkiness about it. However, if I also recall correctly, Jeffrey Steingarten actually preferred his meat aged much longer. Most places will not age meat over 21 days simply because they do not have space or adequate facilities to age meat longer than that. And 21 days is the exception, not the rule.
I've certainly not done a side by side comparison, but the steaks that I've had that were marketed as dry-aged (vs. wet aged) at least 28 days were the best.