[Solved]-On an editable material-table, how can you restrict the user to not be able to enter chars, special characters or negative numbers?-Reactjs

You have the answer in your question. On the column with title Birth Year, the type is set to numeric! :)

You could also add your own custom component for editing each column like so:

{ 
title: 'Birth Year', 
field: 'birthYear', 
editComponent: (props: any) => (
  <Input 
    defaultValue={props.value} 
    onChange={(e) => props.onChange(e.target.value)} 
    type="number"
  /> 
},