Polibi RS-543GPB-GF User guide

Hello! I've reviewed the Assembly Instruction for the WF283524 bed. This document provides important safety guidelines, including information on mattress size, guardrail usage and age restrictions. I'm ready to answer any questions you have about assembling the bed.
What size mattress is recommended for this bed?

What is the minimum distance of the mattress surface below the guardrails?

Is there an age restriction for using the upper bunk?