The Bachelor and the Bobby-Soxer, aka. Bachelor Knight in the UK, from 1947. Starring Cary Grant, Myrna Loy and Shirley Temple.
IMDB storyline: Teenaged Susan Turner, with a severe crush on playboy artist Richard Nugent, sneaks into his apartment to model for him and is found there by her sister Judge Margaret Turner. Threatened with jail, Nugent agrees to date Susan until the crush abates. He counters Susan's comic false sophistication by even more comic put-on teenage mannerisms, with a slapstick climax.
I really liked this movie. I really like Cary Grants movies, and he did well in this movie too. My wife also liked it, so we will definitely see it many times in the years to come. It had a few scratches, and the sound was not crystal clear, but the quality was as expected so it is OK. As it is b/w I don't have to deal with color fade. It was a bit worse that two of the three aluminium reels was dented in the UPS transport. I had to use my Leatherman to bend it back. They are now not as straight as they should be, but works ok.