control_form.js

class Form extends React.Component {
state = {
  cats: [{name:"", age:""}],
  owner: "",
  description: ""
}
handleChange = (e) => {
  if (["name", "age"].includes(e.target.className) ) {
    let cats = [...this.state.cats]   
    cats[e.target.dataset.id][e.target.className] = e.target.value
    this.setState({ cats }, () => console.log(this.state.cats))
  } else {
    this.setState({ [e.target.name]: e.target.value })
  }
}
// ...rest of component