I really don't know how you're suppose to feel at any given age. I'm 49 but still feel the same as I was 30 years ago...outside of a few aches and pains now and then. One good thing about getting older is that I know I'm not as naive as I once was, but I'm still pretty much the same when it comes to values and with time comes wisdom.
I know what you mean about seeing people your own age and even younger and wondering if you look "that old" too. Well, my neighbor for the longest time thought she was 3 or 4 years older than me and it turns out she's that much younger than me and she was shocked. I lay that too having never smoked and I stay out of the sun...I have to due to experiencing a basal cell carcinoma.
I consider myself grown up, my interests have changed but that doesn't mean you should stop having fun!
As far as the period thing...I'm very much ready for that to be over; I've had it way long enough. In fact, if I only knew I'd never would have any more kids after my last son was born, I would have seriously considered asking the doctor to perform a hysterectomy along with my c-section. Think of the years I could have been free!!

Seriously though, I know I'm on the home stretch as far as that goes...I hope

and don't turn into one of those women that still has their period at 56!