This means that compared to other children your childs age he is not speaking or understanding or both at the same level. Start speech therapy as soon as possible so he can make quick progress. Do find out if there are any other issues. Please check with your pediatrician. Good luck.

It means that given 100 children, your child is performing 79th, basically and only 21 children performed worse. Most schools consider having a 50% delay significant to justify special education services, i.e., speech therapy through an IEP (individual education plan). In speech production, most children with this percent of delay, would be difficult to understand.

Hello

These percentages are very non specific. You can see a development specialist for further evaluation.

I assume that he have been evaluated, and treatment recommended (speech therapy) so he can reach 100% if there are not any other medical condition that should be addressed.