I sent some items to sell to Amazons back in September. They’re not selling how do you get your items back? 
Select the item from your inventory page and create a removal order.
One other thing sellers do is figure out how much the removal order would cost per unit and discount it by that amount instead of removing it. If you can afford to absorb the fees for a few more weeks - keep the inventory there until Black Friday and Cyber Monday - maybe it’ll sell then.
I was wondering if you can request a removal order anytime as a seller, even when you are a newbie. Or are there any criteria how old the units must be or selling too slow to be eligible… Can Amazon force you to remove stock if it isn’t selling well?
I am in the process of starting to sell on Amazon, and I am quite worried that I will end up with inventory that doesn’t sell
Yes.
are there any criteria how old the units must be or selling too slow to be eligible
No. You can remove units from FBA at any time. If they are slow moving, you should consider removing them to avoid additional FBA fees.
Can Amazon force you to remove stock if it isn’t selling well?
No. It’s your decision.
I am quite worried that I will end up with inventory that doesn’t sell
That’s a possibility. You could test the market by listing them as FBM and/or send a small quantity. If they sell well send more. If not, it wouldn’t cost you a fortune it they don’t.
Thank you so much!
You’re welcome.
All the best…