He wants to get married but his mother is objecting to that because he is young
Question

                I am nineteen years old, and I want to get married, but my mother does not want me to because she thinks that this is not the time to get married. Is it permissible for a man in Islam to get married without his parents’ agreement and without telling them until things improve, in sha Allaah?.
Praise be to Allah.Firstly: 
It is 
    permissible for a man to get married without his parents’ agreement, unlike 
    a woman, for whose marriage to be valid it is essential that her wali 
    (guardian) agrees. But it is part of honouring one’s parents and treating 
    them kindly to ask for their permission and seek their approval, because 
    that is more likely to keep relationships with them harmonious. 
Secondly: 
You should 
    explain to your mother how great your need for marriage is, and try to 
    convince her and earn her approval. If she responds, then praise be to 
    Allaah, but if she persists in her attitude, then there is no sin on you if 
    you get married to the girl you want, if she is righteous and 
    religiously-committed.  
It is a 
    common mistake for parents to refuse to let their children get married on 
    the basis of studies or their being too young; they do not understand the 
    problems suffered by young men at a time when temptation is widespread. 
    Their refusal may lead to their children going astray and following a path 
    of evil. Hence we advise fathers and mothers to help their sons and 
    daughters to get married, and to make it easy and encourage them to do that, 
    in obedience to the words of the Prophet  (peace and blessings of Allaah 
    be upon him): “O young men, whoever among you can afford to get married, let 
    him do so, and whoever cannot afford it, let him fast, for that will reduce 
    his sexual energy.” Narrated by al-Bukhaari (5065) and Muslim (1400). 
Shaykh Ibn 
    ‘Uthaymeen (may Allaah have mercy on him) was asked about someone who wanted 
    to get married but his parents refused. He replied: 
With regard 
    to this issue, we must offer two pieces of advice. Firstly, we advise your 
    father who insisted on not allowing you to marry this woman whom you 
    describe as being of good character and religiously committed. What he must 
    do is allow you to marry her, unless he has a legitimate shar’i reason which 
    he knows and can explain to you so as to put your mind at rest. He should 
    weigh up this matter himself and imagine if his father had prevented him 
    from marrying a woman whose religious commitment and character he liked, 
    would he not regard that as a disgrace and restriction of his freedom? If he 
    would not like his father to do that to him, then how can he agree to do 
    that to his son? The Prophet  (peace and blessings of Allaah be upon 
    him) said: “No one of you truly believes until he likes for his brother what 
    he likes for himself.” 
It is not 
    permissible for your father to prevent you from getting married to this 
    woman with no legitimate shar’i reason. If there is a legitimate shar’i 
    reason, then let him explain it to you so that you will understand. 
And our 
    advice to you is: if you can find another woman instead of this woman, and 
    please your father and maintain a harmonious relationship with the family, 
    then do so. 
But if you 
    cannot do that because your heart is attached to her, and you are afraid 
    that if you propose to another woman that your father will prevent you from 
    marrying her too – because some people may feel jealous even towards their 
    children and prevent them from doing what they want – then I say: if you are 
    afraid of that and you cannot do without this woman to whom your heart is 
    attached, then there is no sin on you if you marry her, even if your parents 
    object. Perhaps after you get married he will accept what has happened and 
    what is in his heart will go away. We ask Allaah to decree for you that 
    which is best for you. 
End quote 
    from Fataawa Islamiyyah (4/193) 
And Allaah 
    knows best.