Morita has a younger girlfriend.
Koichi is 38 years younger than Arnold Schwarzenegger.
Even though that kid is younger, he’s really mature.
When you have someone who has years below your own, this person is younger than you.
The reading for this one is kind of strange. It is the kun'yomi reading for both of the kanji. You know the kun'yomi readings from earlier, back when you learned the vocab 年 and 下.