When I posted this originally in lgbtq 1 user accused the song of being pedo… so I posted more context and I’ll post that context here as well.
Little can refer to someone's height or weight. Think of it this way, there's a phrase that goes "Ain't you a pretty little thing?!". That phrase, while maybe a little outdated, is talking about a girl's or woman's appearance and weight/height being pleasing to the person who said it. In this context, "little" has nothing to do with her age.
Also, back then if someone is "your girl" it meant that you were exclusively seeing each other like you are a couple. Even today you have the term girlfriend which also uses girl in the word and doesn't refer to someone's age. Adults for example don't call their partners their manfriends and womanfriends...
For more context, the song its self is from one of Elvis' movies and both love interests are not minors. Elvis' movie character is just singing a song about having feelings for two beautiful women and terminology changes over time.
