Individual experiences vary widely; I am 41 now and still have just as much trouble going to bed before midnight or waking up before 9 as I did in my 20s. It still takes effort to restrain my impulse to stay up all night, in fact, whenever there's something remotely interesting or creative I could be working on instead of sleeping. It is not simply a matter of habits, either; I spent most of seven years getting up in time for a 7 AM conference call every work day, and it never got any easier. As soon as that was over, I went right back to my old schedule.

Perhaps it's less of a struggle to fit my life into normal business hours now, after years of experience trying to do it, but that's really just a matter of coping skills; my body clock remains as stubbornly nocturnal as it has ever been.