If your levels decline, which they likely will, they will also likely return to baseline. There is always the possibility when using anything hormonal that you may not return to baseline. This is the risk you take when running anything hormonal, including ostarine, even though it's not a hormone itself.
Look, it's all about pros and cons and weighing them out. Is the risk worth the reward for you? That's up to you, not us. Will you rebound, more than likely, even without a PCT. People always get their forum panties in a bunch when I say that. Let me be clear, I'm not recommending not using a PCT but even without one you would still more than likely rebound.
Your body wants to return to baseline just as badly as you want it to and will take the necessary actions to do so. All of that being said, you're 20, I don't think you should take them. I don't think a lot of people should have run the cycles they have at their stage in the game but instead of trying to scare you out of it, I thought it better to let you know why.
Black and white, you take it you'll more than likely rebound, BUT you could end up falling in the group that runs into issues. Risk vs reward.