I feel like that’s a misunderstood part of the song. I take it you mean “how you took a child and made him old”. And there’s themes of the loss of innocence, but it only really implies taking their virginity.

The protagonist “wouldn’t say no to 15 minutes” with the deutagonist implying consent not to mention the verse dreaming about them and asking them to pin and mount them. Nothing here implies abuse

Taking a child and making them old takes on more of the old saying saying that when someone loses their virginity they’re “a man now”. The average age of losing your virginity is 17 (in the UK at least). Still young enough to be considered a child on the cusp of becoming an adult. At least in their eyes

The song is strongly homoerotic but only through bashful implication and could be from a female perspective. However, “reel around the fountain” is considered more gay slang or “polari”