The mistake

Question

https://code.sololearn.com/Wm22MnH9HgEh/?ref=app

Answer 1

<input type="textbox" id="age">
<input type="button" onclick="age()" value="check">

Answer 2

Manar Hasanen

Where did you get value of textbox?

where did you define age variable and store value of textbox?

To get textbox value do this:

var age = Number(document.getElementById('age').value);