Truthfully, I thought you were older than your actual age.
The people guessing in real life see you in action though. Possibly you give off more youthful vibes from your actions, language and gestures - so rather than being an exhausted mum, you're actually coming across as someone with lots of energy.
I wouldn't say that they're lying, more that they're ageing you based on more than your looks, and you clearly come across as someone who hasn't given up on life. It's a compliment, and it's more meaningful than how many wrinkles you do or don't have. Actually acting young is what keeps us young, and that's what keeps us healthy.