I cant speak for Nate but I started (unknowingly, although I should've researched) at 17. However I stopped till 21 after that 1st cycle. I cant "notice" anything per say and luckily bloods have come back fine. But ive seen so many people start young saying they'll only do "one" cycle and fall into a vicious and reckless cycle of abusing hormones, and mess themselves up pretty bad. You have amazing genetics and/or work ethic and can tap into your high hormonal levels for years to come. Take advantage of it, keep up your hard work and reevaluate later down the road.