Hi Koko2,
I was always mistaken for being in my 20's, until my girls were a couple of years old (and I was in my late 30's). For around 5 years, people weren't shocked by my age...which made me sad. A little part of myself has always enjoyed looking younger than others my age, and those who are 10 years younger!
My physique really didn't change ~ except I was a bit thinner during those years. The only difference that I can think of is that my girls were a huge stress upon me back then. I also had a lot of other stressors (physical and emotional) back then.
I'm 41 now, and people are once again shocked to hear my age. Hopefully, things will turn around for you too!