I didn't start to really notice these changes until 40 and, like you said, it seemed to happen on my 40th birthday - weight gain, impatience and, for me, my skin texture changed and I became more achy and less agile than I was before.
Then again, I am also much more confident than I was when I was younger and feel I have a much better grip on who I am and what I want. I wouldn't trade that for anything. So, I accept all the changes and enjoy feeling more comfortable in my own (older) skin.
