He is twenty years old… and he has not been circumcised
Question

I am a young man aged 20. I had an operation when I was little and for that reason I was not circumcised. After that I went to the hospital and the doctor told me that I had to do the operation first because of a physical defect in the same area, then I should be circumcised. Years have gone by and I have not done the first operation and so I have not yet been circumcised. I have reached the age of twenty and this is my situation, and I pray in the mosque. What is the ruling in this case?.
Praise be to Allah.Circumcision is obligatory for men according to the majority of scholars, and it is one of the sunan al-fitrah (the actions connected to the sound nature of man), as the Prophet (peace and blessings of Allah be upon him) said: “The actions of the fitrah are five: circumcision, shaving the pubic hair, trimming the moustache, clipping the nails and plucking the armpit hairs.” Narrated by al-Bukhaari, 5441; Muslim, 377. 
Al-Bukhaari (3107) and Muslim (4368) narrated that Abu Hurayrah (may Allah be pleased with him) said: The Messenger of Allah (peace and blessings of Allah be upon him) said: “Ibraaheem (peace be upon him) circumcised himself when he was eighty years old.” 
But that fuqaha’ have stated that if an adult fears that circumcision may harm him, then it is waived in his case. Ibn Qudaamah (may Allah be pleased with him) said: “Section: With regard to circumcision, it is obligatory for men and an honour for women, but is not obligatory for them. This is the view of many of the scholars. Ahmad said: It is more obligatory for a man, because if a man is not circumcised, then that skin is covering the glans and it cannot be cleaned properly. And it is less important for women.” 
Abu ‘Abd-Allah (i.e., Imam Ahmad) said: Ibn ‘Abbaas was very strict on this issue. It was narrated from him that there is no Hajj and no prayer for one who is not circumcised. But al-Hasan granted a concession with regard to that, and said: If a person becomes Muslim, it does not matter if he is not circumcised. He said: Black and white people became Muslim, and no one examined them, and they did not get circumcised. The evidence that it is obligatory is that covering the ‘awrah is obligatory, and if it were not for the fact that circumcision is obligatory it would not be permissible to transgress the sanctity of the person being circumcised and look at his ‘awrah in order to carry out this procedure. And this is one of the symbols of the Muslims. So it is obligatory, as are all the other symbols of Islam. If an adult man becomes a Muslim and he fears that being circumcised will harm him, it is waived in his case, because ghusl and wudoo’, etc are also waived if there is the fear that they will cause harm, so it is more appropriate that circumcision be waived (in this case). If a person is sure that he will not be harmed by it, then he has to do it. Hanbal said: I asked Abu ‘Abd-Allah about the dhimmi (Jew or Christian living under Islamic rule) who becomes a Muslim: Do you think that he needs to be circumcised? He said: It is essential. I said: Even if he or she is old? He said: I like for him to be purified by that, because of the hadeeth:  “Ibraaheem (peace be upon him) circumcised himself when he was eighty years old.” And Allah says (interpretation of the meaning): “it is the religion of your father Ibraaheem (Abraham)” [al-Hajj 22:78]. 
From al-Mughni, 1/101 
It says in Fataawa al-Lajnah al-Daa’imah (5/113): 
Circumcision is one of the Sunnahs of the Fitrah, for both males and females, but it is obligatory for males and a Sunnah and an honour for women. 
With the advances in the field of medicine, circumcision has become a safe procedure in most cases, so you should hasten to get circumcised and fulfil this obligation, follow the example of the Prophets, preserve your sound human nature (fitrah) and be on the safe side with regard to worship. 
And Allah knows best.