Sugar OP. Give up/massively cut down on sugar.
Don't know if you're a sugar nut like me but I see a MASSIVE difference in my skin when I stop eating it. I'm 41 and like you I had a sudden moment last year, not long after I turned 40, when I suddenly looked in the mirror and couldn't believe how OLD I looked. Washed out and pasty and flabby in the face (though I wasn't overweight) and just old.
My diet was sugar heavy and I just (with a bit of effort) stopped as much sugar as I possibly could.
Upped the veg, especially green veg, a lot.
Started walking wherever poss for exercise, an hour a day or more if I can.
The difference when I do this is amazing. Within a week or so of cutting down the sugar/upping the veg, my skin starts to glow again. If I go back on a sugary diet, within a few days, I look rubbish again.
Oh and though I hate typing this as it makes me feel like I'm turning into my mum - wear colour, if you don't already. It has taken me a few months to notice that my 'old' staples of white shirts, grey tops etc, can just make me look haggard, old, tired. I have ditched white and all the pale cream colours I used to love and that suited me. Reduced grey. Oddly I have gone back to black which I stopped wearing in my mid-30s as I thought it was ageing but now it seems to work again, in an austere sort of way that I quite like. BUT to return to my point - colour! I now wear, amazingly to myself, quite bright greens, yellows, even warm orange. Not head to toe, obv, and with dark neutrals. But near my face, a shot of the right bright works wonders.
Hair is important too, I've gone a fraction darker with a semi-permanent gloss which surprises me by helping, i assumed I'd have to go blonder as I got older but the slightly darker colour (which also fades greys) works on me.
It's small tweaks, really. Nothing expensive or drastic. the sugar thing, i think, is key.
The only expensive thing I now do is useEmma Hardie moringa balm cleanser which is honestly a miracle in a jar (along with the no sugar thing obv).
I can't really afford facials but I had one as a gift card and it was a nice lift. an anti-ageing facial would probably make a nice difference if you could afford a regular one.
Good luck! Green veg! No/less sugar!
THat's my tuppence worth, anyway!