Honestly, OP, at 42 you are pretty much still in your prime!
You will look back and wonder what you were upset about.
I am almost 25 years older.
People who don't know me (genuinely) think I am 50. I get ID'd when I have to ask for concessions.
I am lucky that all the women in my family have youthful genes BUT I can share some of my own tips.
I don't drink- can't for medical reasons and stopped at 40.
I use sun block every single day and have since 37 when I had a skin condition and treatment included sun block and I've just carried on.
I eat very healthily. Avoid almost all refined carbs, sugar, fizzy drinks etc except for the odd treat.
I am the same weight within about 3-4 lbs that I was in my 20s.
I keep up to date with make up trends and use make up daily (usually Bobbi Brown as I like a natural look.)
My hair colour has faded from dark auburn but I have a few lowlights a couple of times a year and I've grown out the short cut I had at 45.
Honestly, you CAN do this! You won't look 20 but you will look the best for your age.
and as for Helen Mirren, she has had countless face lifts and she doesn't look great even now. She has presence but that's her confidence coming over.