open System

let rec readAge () : int =
    printf "Age: "
    match Int32.TryParse(Console.ReadLine()) with
    | true, age when age > 0 -> age
    | _ ->
        printfn "Cannot read the age, please retry.."
        readAge ()

let readNextPerson () : (string * int) option  =
    printf "Name (empty to stop inputs): "
    let name = Console.ReadLine().Trim()
    if name = "" then None
    else Some (name, readAge())

let rec readPersons () : (string * int) list =
    match readNextPerson() with
    | Some p -> p :: readPersons()
    | None -> []

let printPerson (name, age) =
    printfn "name: %s (%s)" name (if age >= 20 then "no longer a teenager" elif age >= 13 then "teenager" else "child")

[<EntryPoint>]
let main argv =
    for p in readPersons() do
        printPerson p
    Console.ReadKey() |> ignore
    0