function to get input group for user
DOM
The outer HTML conversion is probably unecessary. You can manipulate DOM nodes directly. The appending could look something like this.
// note that the HTML representation is irrelevant; we go straight to the DOM
document.getElementById('input-groups').appendChild(ageCol)

JS
addInputGroup() seems to be a misleading name, as the function creates a new DOM element; it doesn't do anything with it. createInputGroup() would be more appropriate I think.
You can use const instead of let here. This provides some nice guarantees about consistency, and makes these guarantees immediately visible to the reader.
return(ageCol.outerHTML); is more commonly written as return ageCol.outerHTML;