All the twenty something's reading this thread now with fear in their hearts 
It happens fast!
I'm 32. I don't feel anywhere near as stunning like I did at 25. I don't turn every head in the room anymore - nobody in their twenties make much effort to look now unless I'm wearing tight clothing. What a difference a couple of years makes!
Having a baby at 29 aged me fast but it wasn't in a way I could put my finger on...didn't have wrinkles for example. But I would do my make up the same and instead at the end of it looking and thinking beautiful! I just began to think...meh. Not bad. That'll do. I looked the same...but didn't look the same?
(The plumpness of youth does have a certain beauty btw that is true, but you lose it fast.)
I then began scrutinising and recognised everything different. Volume loss in certain areas of face making cheekbones too prominent, and hollower under eyes, very slightly lowered eyebrows/eyelids very slightly sagging, mouth corners not quite as turned up as before, very fine lines, volume loss more prominent from nose to chin (nasolabial) hair line has receded....etc I suddenly saw it all.
These things don't smack anyone in the face when I meet them as they are all subtle right now. Nobody would think I have sagging eyelids at all. It just means they recognise I'm about 30 rather than 20. Which is normal. Nobody actually looks ten years younger btw people are exaggerating and being complimentary. Maybe a few or five years max, but not ten... mostly they just look good for their age. Which is great!! It's much easier to look older than your years.
Sometimes I do have a little freak out because I know it all becomes more and more prominent with age, (overnight sometimes!) and I worry I will wake up a completely different person - it's all about a loss of control. Even my neck skin under chin stretches when I look over my shoulders now, and I think I will have a lovely full on turkey neck one day soon and it's all completely out of my claws hands.
I then realised this happens to literally everyone (if you're lucky) and your twenties are over and done in the blink of an eye for us all. I have started to tell myself that these changes are okay. I think I fear them not just because of 'losing looks' but because it means getting old which means possible suffering, and of course inevitable death. The reality is that that is likely far off! And I'm pretty sure every decade that passes I will look back and think how young I looked and why did I fret.