But yes, in the U.S. a brand-new 28 year old Ph.D. may well be an Assistant Professor, and essentially all those teaching have some type of 'professor' title (save Lecturers, Instructors, and Research Associates). This is very different from in Europe, where you may well have only one Professor per dept., or at least per major area within that field--though I understand title inflation is hitting over there now too.
The European system is very different from the US (and, increasingly, the British) systems. I've taught in German universities on multiple occasions over the years and still don't feel I understand it (there are multiple affilations people have with working groups, research centers, universities, and so on, which have different degrees of structural permanence but which are nonetheless real elements in people's academic affiliation, in a way that's not true at all here, where your one permanent affiliation is to your own department). Things are changing, it's true; but the normal MO over there is, as Arni has said, to have a single full professor per program, with a bunch of assistants, usually on soft money and nonpermanent contract, floating around like increasingly desperate moths around a flame waiting for a Professorship to open up—as a rule, well out in the provinces; the ones in e.g. Munich or Berlin will have an already very senior person well at the head of the line, so you may well wind up at Bochum in the Ruhr or somewhere else in the sticks, at least for your first job. But once you're a Professor in Germany, you're set for life... except that now your job becomes scrambling around, full-time, to dig up the money, essentially all of which comes from the German government, to fund your own swarm of assistants who now depend on
you for the food on their table. In a lot of ways, it's a good deal more brutal a system than ours here, though in other respects, given the much thicker social-service carpeting over there, you're in better shape if the worst happens and you wind up without a job... in any case, make no mistake: in much of Europe, call yourself a Professor without the academic credentials and you are going to be a laughingstock, and possibly in serious legal trouble as well. It's a different world over there...