I've always liked my body, even as a teenager, but I suspect my liking has a great deal to do with my measuring stick.
Since my broad shouldered IT body shape never fit conventional feminine norms, I've always been more interested in clothing it for a functional, active lifestyle than for fashion. I suspect this focus insulated me from a lot of the body image angst which was rampant in my peers. I was also lucky enough to marry a man who admired my strength, fitness, and endurance. As the sole female in a family of males, I could keep up with them and enjoy the activities they enjoyed.
It was only in my forties, when I had more time to spend with my girlfriends and to play with fashion, that I realized how out of step I was with prevailing female norms.. Most non-athletic clothes were not cut for my body--my shoulders were too wide, my arms and legs were too muscular, my waistline was too large and in the "wrong" place, my feet were too large--the list of ways my body wasn't "right" was so alarming it was almost laughable. And, as if that wasn't enough, the first signs of aging were starting to appear.
I honestly think it was the overwhelming number of ways my body wasn't going to fit into prevailing norms of feminine beauty that made me just turn away from the whole cultural expectations thing. I had zero interest in re-shaping and re-designing a functional body I had enjoyed inhabiting for almost half a century just to fit some arbitrary notion of feminine beauty.
By my standards, I'm just fine as I am--and my liking extends to the signs of aging I'm seeing as the years pile on. I'm more interested in keeping my body strong and flexible than I am with fighting wrinkles and cellulite.