What age to start tretinoin/retinoids

Good evening, I am in my early twenties and I have using the naturium retinol complex serum for a few months, I noticed retinol is amazing for my skin and I wanted to up the percentage, browsing online I found out that tretinoin is the best option but I was wondering, is it too early to start?Will I build some resistance to it? I plan on buying the 0.02% which is available otc in my country but I don't want to up the percentage(because that's not available otc). Is using the same percentage of tret my whole life effective? Will I have to go higher?Will I still get anti aging benefits over time? My point is, I am down to start tret now because prevention is important but I don't want to have to up the percentage down the line,so should I keep using cosmetic retinols and wait till I get older to start to get into retinoids?Please give me some advice.