open System

type PersonInfo = string * int

let isValidAge age = age > 0 && age < 120

let rec readAge name =
  printf "Enter age of %s: " name
  let success, keyIn = Int32.TryParse(Console.ReadLine())
  if success &&  isValidAge keyIn
  then keyIn
  else
    printfn "Invalid age!"
    readAge name

let rec readPeople (people : PersonInfo[]) : PersonInfo[] =
  printf "Enter Person name (enter . for quit): "
  let name = Console.ReadLine()
  if name = "." || String.IsNullOrEmpty(name)
  then people
  else
    let age = readAge name
    Array.append (readPeople people)  [|(name, age)|]

let printPerson person =
  let name, age = person
  if age >= 20
  then printfn "%s is %i years old and not longer a teenager." name age
  elif age > 13 && age < 20
  then printfn "%s is %i years old and therefore a teenager" name age
  elif age = 1
  then printfn "%s is %i year old and therefore a child" name age
  else printfn "%s is %i years old and therefore a child" name age

[<EntryPoint>]
let main argv =
  readPeople [||]
  |> Array.rev
  |> Seq.iter printPerson
  0 // return an integer exit code