Ah, but being 40 means you are so much wiser
I am closer to 50 than 40 now with an almost 2 year old and in the process of adopting another infant. I was raising my boys in my 20's and 30's and I can say without a doubt that I am much more confident and can let things roll off my back much easier now than I did when I was younger.
The weight thing? Yes, that's a struggle and I just recently took up bike riding. My body hurts pretty much from the waist down, but it's the first time in my life that I've been aware of just how much better I feel when I've gotten up off the chair and moved.