我们可以用 "He is in the habit of staying up late" 来描述一个人经常熬夜。

"Habit" 是一个名词，指一个人经常重复的行为或习惯。例如：

I'm trying to break the habit of procrastination. (我正在努力克服拖延症。)
Smoking is a bad habit that can cause serious health problems. (吸烟是一个有害健康的坏习惯。)

"Stay up late" 是一个动词短语，指经常在很晚的时候睡觉。例如：

I usually stay up late on weekends to catch up on my favorite TV shows. (我通常在周末熬夜看我最喜欢的电视节目。)
Staying up late can have negative effects on your health and wellbeing. (熬夜会对你的健康和幸福造成负面影响。)

希望这些信息能帮到你。