Candy Clark weird casting for the stepmom (too old)

The Christopher Walken character says his woman is only about five years older than his son. I immediately thought she certainly didn't look that young, but I wondered if maybe it was just her hairdo that dated her and made her look older. Nope, the actor (Candy Clark) is actually 13 years older than Sean Penn, and only four years younger than Christopher Walken. She was in her forties when this movie came out. She looks a bit younger than she is, and certainly has a good body especially for her age, but the script implies her character to be almost twenty years younger than Clark is, and she just doesn't pass for someone in her early twenties (no shade on her: even on a show like 90210 I don't think anyone ever tried to pass for quite THAT much younger).

If they were really sold on casting her, they should have taken that line out of the screenplay.