I am in my early 60’s and have never had dark spots. I dont know if its because I have always looked after my skin and used a sunscreen ever since I was in my early teens (thanks Mum).
There are a couple of products that I use in my skincare routine on rotation and one if the Swisse Vitamin C 10% Brightening Booster Serum. I figure Swisse know vitamins.
Another is Garnier green labs Brightening Serum Cream which is a moisturiser, serum and sunscreen all in one. It says on the box Pinea-C (Vitamin c + Pineapple)