Do you wear sunscreen OP? That would be a good place to start. Especially if you are going to use any retinoid product. Any of them will make your skin more susceptible to sun damage, so you would need to start using a high SPF everyday.
You could start with over the counter retinols, especially if you have sensitive skin as they are less irritating. But they are also less effective - tretinoin (a prescription strength retinoid) is basically the concentrated version - it's thought to be up to 20 times more effective than OTC retinols. That's because the OTC ones have to go through some metabolic conversions in your skin to get to the active ingredient (retinoic acid). Whereas tretinoin is retinoic acid.
The reason it's only available on prescription is that it's basically a medication in cream form, so can be quite harsh. It was trialled as acne medication decades ago, and have many years of clinical research behind it proving its' efficacy.
It is brilliant (once your skin tolerates it) for increasing cellular turnover, which slows down as we age, and increasing collagen production, which also slows as we age.
Some people get on fine with OTC retinol and don't want to bother with the super strong stuff, as tretinoin is definitely more irritating on your skin at first and can cause purging (flaky dry skin, redness, irritation) sometimes for several weeks or even months before your skin adjusts. Something to think about if you have a big event coming up.
But if you are in the UK and want a prescription strength, you can try Skin & Me or Dermatica, they both do a subscription service for tretinoin. Or you can try getting it from some online pharmacies.