When Should a Son Stop Sleeping in the Same Bed with His Mother in Islam?
Question

I am nineteen years old and I want to know: is it permissible for me to lie in the same bed as my mother at night? My question is because I have reached the age of nineteen years and have passed the age of puberty.
Praise be to Allah.The answer to this question is based on the hadith of `Abdullah ibn `Amr ibn Al-`Aas (may Allah be pleased with him) who said: The Messenger of Allah (blessings and peace of Allah be upon him) said: “Teach your children to pray when they are seven years old, and smack them (lightly) if they do not (pray) when they are ten years old, and separate them in their beds.” (Narrated by Abu Dawud, 495; classed as authentic by Al-Albani in Sahih Abu Dawud) 
This separation of children includes all children : males with males and with females; and females with females and with males. If separating between them is obligatory when they are at this age, then it is even more essential after that, because desire grows more intense. 
This Hadith is a response to those who say that there is no desire among Mahrams, and it is what motivated some scholars to say it is allowed for an adult male to sleep in the same bed as his mother or his father. But the correct view is something other than this. The one who ponders how things are nowadays will not doubt that the correct way is to prevent that, and that the Hadith includes a grown son sleeping in the same bed as his mother or his father, and a grown daughter sleeping in the same bed as her mother or her father. 
Ibn `Abdin Al-Hanafi (may Allah have mercy on him) said: 
“In Al-Bazariyyah it says: When the boy reaches the age of ten, he should not sleep in the same bed as his mother or his sister or any woman other than his wife.” 
What is meant is that they should be separated when sleeping for fear of falling into forbidden actions. When a boy reaches the age of ten, he understands sex but has no religious commitment to keep him away from it, and if he sleeps in the same bed he may end up being intimate with his sister or his mother. 
Sleep is a time of rest and provocation of desire, in which the garments are removed from the `Awrah by both parties, so it may lead to prohibited things and forbidden intimacy, especially in these times when they know more of immorality than adults do!” (Hashiyat Ibn `Abdin, 6/382) Ibn `Aabdin died in 1252 AH.
An-Nawawi (may Allah have mercy on him) said: 
“It is not permissible for a man to lie down with a man or for a woman to lie down with a woman, even if one is on one side of the bed. When boys and girls reach the age of ten years, it is essential to separate the boy from his mother, father, sister and brother when sleeping .” (Rawdat At-Talibin, 7/28) 
An-Nafrawi Al-Maliki (may Allah have mercy on him) says in Al-Fawakih Ad-Dawani (2/312): 
“With regard to a male and a female lying next to one another, there should be no doubt that it is prohibited for them to lie next to one another under one cover even if the `Awrah is covered or even there is a barrier, if they have reached the age of puberty.” 
To sum up, it is not permissible for you to sleep in the same bed as your mother; rather you have to sleep in a separate bed. 
And Allah knows best.