Genes! Sorry probably not what you want to hear.
My gran on my mothers side (that's where the youthful looks are) was very into taking care of herself and had a "regime" but her mother and my mother did nothing more than wash with soap and water and look just as good. My mum has the most amazing soft smooth skin and always has. When I was getting married, bro finishing police training and sis leaving school she mentioned this to a colleague and colleague genuinely assumed she'd had me/us very young for all that to be possible, perhaps even underage! She actually had us quite "late" for her family being mid 20's (catholic family previous generations all married and mothers much younger), but I also think it's the bone structure and features that make us look younger.
My skin isn't the best due to mh issues, but prior to that I've often been mistaken for being much younger than I am, I was still getting not only ID'd but automatically given child fares on public transport until my early 30's.
When pregnant with dd (late 20's) I had some odd/nasty comments made by strangers when I was heavily pregnant and not wearing my wedding ring (fingers were swollen it ended up on necklace).
Dd is almost 19 and TALL and still gets taken for 14/15 max she is finding it frustrating just now but will enjoy it more as she ages.
On the downside the same genes also seem to come (in our family at least) with apple shaped figure and a real struggle to keep weight down. Which aside from the looks aspect also makes us more prone to developing diabetes even in those family members that have managed to maintain a healthy weight and diet.
I happen to think even type 2 diabetes isn't solely down to poor behaviour based on that experience, else everyone that's overweight with a sweet tooth would get it.