I think it's natural, especially given all the pressure society puts on women to look youthful, and the hyper-attention placed on our looks in general, for it to feel rather disturbing when our bodies change. But hopefully, over time we come to accept it, and these changes become less and less disturbing.
I didn't freak out about turning 40 last month. Part of the reason is because no one would guess I'm 40 anyway (which really, is a little stupid, because of course 40 can look like me, 40 can look lots of ways! and don't make me paranoid for when the time comes that you actually do think I look 40, people! and give me credit for the 40 years of experience I have living life!), but the other reason I didn't freak out, I'll take credit for:
I've tried to follow my dreams and not live on someone else's timeline.*
I try not to judge myself based on traditional measures of success (career, marriage, children, money, etc.), but on what makes me feel fulfilled and like a good person. It's super hard taking this road, but it is the one for me. When I don't follow my instincts and try to do the "sensible" thing, because I feel pressured to do so or because I can't see another option, I always regret it. (Not saying there is anything at all wrong with focusing on the above things! Most of them are just not my dreams/goals, not so far.)
*Yes, there have been prices to pay for living this way, such as being poor and having no financial security :/ but that could change. There are prices to pay when I give in to a more traditional life too.