At 14, you really don't need to go crazy on AHA products! Make sure you start slow (once a week) and don't overexfoliate as that can cause irritation to your skin.

Get Sunday Riley Good Genes. I wrote a review on this if you want to take a look, it is SO effective with dark spots. Also, to echo others, please make sure you are wearing sunscreen! This is step #0 before anything else.

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  SUNDAY RILEY Good Genes All-In-One Lactic Acid Treatment

Niacinamide is great for fading dark spots–I've had a good experience with Glossier's serum. The serum from The Ordinary seems to be popular and just as effective at a budget friendly price! Also, make sure you wear sunscreen! All efforts are pretty meaningless if you're not protecting your skin from the sun.

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  The Ordinary Niacinamide 10% + Zinc 1%

I've heard amazing things about this Farmacy serum for treating dark spots and even skin tone! It's on my list.

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  Farmacy Honeymoon Glow Aha Resurfacing Night Serum With Hydrating Honey + Gentle Flower Acids

Try incorporating a AHA chemical exfoliator into your routine! AHA will help your skin exfoliate and hell with skin turnover, which will aid in fading dark spots. I really like Pixi Glow Tonic. But any product with AHA would work!

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  Pixi Glow Tonic
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  COSRX Aha/Bha Clarifying Treatment Toner