Im making an age number for the character (Basically how old the player starts as.)

I was wondering how the input script would only accept numbers.

You can use the IsInt function to test if a string is a valid number; and ToInt to convert a string to a number.

So you could have a function that does something like:

msg ("What is your age?")
get input {
  if (IsInt (result)) {
    age = ToInt (result)
    if (age > 10 and age < 99) {
      player.age = age
      // If you want to ask another question after this one, you'd do it here
    }
    else {
      msg ("That's not a sensible age")
    }
  }
  if (not HasInt (player, "age")) {
    AskForAge
  }
}

(Assuming that AskForAge is the name of the function, so if the player enters something that isn't a number, or 0, or something that isn't valid, you ask the question again)