Anecdotally I feel I noticed a very fast ageing speed between 38 and 40. Suddenly got white hairs, feel more tired, more wrinkles, way harder to keep VO2max up (I run a lot), muscle sores after training suddenly lasting up to 3 days instead of 1, face looks older, etc.
I feel like that all happened real fast around this age.
It's like there's two versions of me now, the one who was somehow moderately fit by biochemical decree, with a healthy amount of flesh to his face, voluminous dark blonde hair and a pleasant complexion...
... And the grey haired, weathered, lined, dessicated mummy I see in the mirror. I love my kids dearly but the constant caring really takes something out of you. That and the whole getting older thing in TFA.
I keep telling myself I'll get a gym membership soon to reclaim some of my dignity.
Now that they are older I have more free time. Once they get to the point where they can stay home alone things become much easier. For me that was around when they hit 10. I'm 46 now and in the best shape of my life. Keep pushing through, there is light at the end of the tunnel