The T being added in is what? Maybe fifteen years old?
This didn’t sound right to me, I’m sure I heard LGBT more than 15 years ago, so I looked it up. According to Wikipedia LGBT was first used around 1988 but OED says 1992, other sources say it became widespread in either the 90s or 00s (varies by source). So 15 is a lower bound for widespread usage but I don’t think we can get much more specific than “15 to 35 years ago”.
Trans men and castrated men exist, I don’t think it’s the balls.