除了個人體質差異，影響睡眠還有一個很主要的因素就是年紀。從十歲以後，我們會越來越晚睡，男性在 21 歲的時候會是最晚睡的階段，而女性會在 19 歲達到晚睡高峰。There's another factor, which is how old we are. So from about the age of 10, there's a tendency to want to go to bed later and later and later, peaks in lateness in males about 21, 21 and a half in females about 19.