The age at which the phase of youth ends
25-3-2014 | IslamWeb
Question:
Assalamu Alaikum, at what age in Islam does youth end as everyone will be asked how they spent their youth?
Answer:
All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.
summarized the different opinions in his book Al-Mufhim. He wrote: “He is called a “Child” until the age of sixteen, then a “young man” until the age of thirty-two, and then he is called an “old man”. Az-Zamakhshari held that youth starts from reaching puberty until the age of thirty-two. The Maaliki scholar Ibn Shaas said in his book Al-Jawaahir that youth ends at the age of forty. An-Nawawi said that the sound preferred opinion is that youth starts upon reaching puberty and is over until reaching the age of thirty.”
We would like to point out to the questioner that the fact that a person will be asked about his youth does not mean that he will not be asked about the rest of his life. There is no better proof for that than the fact that a person will be asked about both his life and his youth on the Day of Resurrection. Ibn Mas‘ood 
reported that the Prophet, sallallaahu ‘alayhi wa sallam, said: “The feet of the son of Aadam (Adam) shall not move from before his Lord on the Day of Judgment until he is asked about five things: about his life and what he did with it, about his youth and what he wore it out in, about his wealth how he earned it and how he spent it, and what he did with what he knew.” [At-Tirmithi]
However, given the significance of this phase of a person’s life - namely, youth - the Prophet, sallallaahu ‘alayhi wa sallam, made mention of it in specific. Youth is the time of strength when the person is able to carry out acts of worship that require physical strength. ‘Ali Mulla Al-Qaari commented on the Hadeeth saying, “The words of the Prophet, sallallaahu ‘alayhi wa sallam, ‘and about his youth,’ mean that a person shall be asked about his strength in his youth; he shall be questioned about the way he had spent it and whether he had wasted his youth or not. This serves as specifying after generalizing. It is indicative of the fact that one’s bad deeds committed during childhood or old age are more likely to be forgiven compared to those committed during his youth. At-Teebi said, ‘If one says that youth is part of a person’s life so why is it specified in the Hadeeth? The answer is that the Hadeeth refers to the fact that the person will be held accountable for his strength and time during his youth in particular because he is more able to perform the greatest amount of worship that requires physical strength during that phase.” [Mirqaat Al-Mafaateeh Sharh Mishkaat Al-Masaabeeh]
Allaah Knows best.