If I could intrude a note of seriousness into this frivolous conversation...
我真想说一句, 叫他们谈话放严肃些....
I think there is a kernel of truth in these otherwise frivolous comments.
我认为在这些本来是无关紧要的评论中含有一定的真实性。
At 18, he's still rather frivolous and needs to grow up.
他到了十八岁仍然很不懂事,很不成熟。