Lisp's type system is fine.

    (defstruct adult (name 'error :type string) (age 'error :type (integer 18 200)))

    * (make-adult :name "Bob" :age 3)

    debugger invoked on a TYPE-ERROR @5529ACEE in thread
    #<THREAD tid=426288 "main thread" RUNNING {1003F000A3}>:
      The value
        3
      is not of type
        (INTEGER 18 200)
      when setting slot AGE of structure ADULT


    * (make-adult :age 18)

    debugger invoked on a TYPE-ERROR @5529ACF2 in thread
    #<THREAD tid=426288 "main thread" RUNNING {1003F000A3}>:
      The value
        ERROR
      is not of type
        STRING
      when setting slot NAME of structure ADULT