The vast majority of Muslims circumcise their sons in infancy, while some Muslims in North Africa and other places who blindly follow the Maliki jurisprudence, do not circumcise their boys until they reach puberty or a more advanced age.
However, the Sunnah of the Prophet (Sallallahu alayhi wa ala aalihi wasallam) is to circumcise on the seventh day, coinciding with the Aqiqah:
عَنْ جَابِرٍ ، قَالَ : " عَقَّ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ عَنِ الْحَسَنِ وَالْحُسَيْنِ وَخَتَنَهُمَا لِسَبْعَةِ أَيَّامٍ "
Translation: Jabir (r.a.) narrates that the Messenger of Allah (Sallallahu alayhi wasallam) performed the Aqiqah for al-Hasan and al-Hussayn (Radiyallahu anhuma), and circumcised them both on the seventh day. [Sunan al-Kubra of Bayhaqi]
In another Hadith, the Prophet (Sallallahu alayhi wasallam) said:
" مَعَ الْغُلَامِ عَقِيقَةٌ فَأَهْرِيقُوا عَنْهُ دَمًا وَأَمِيطُوا عَنْهُ الْأَذَى "
Translation: “The Aqiqah is ordained for the boy, so shed blood on his behalf, and remove the harmful thing (i.e. foreskin) from him.” (Sahih al-Bukhari; Kitab ul 'Aqeeqah)
However, according to the Maliki jurisprudence, to act upon the Sunnah of circumcising on the seventh day is Makruh (disliked). They argue that it is resembling the Jews (even though the Jews circumcise on the eighth day and not on the seventh):
وَيُكْرَهُ أَنْ يُخْتَنَ يَوْمَ يُولَدُ أَوْ يَوْمَ سَابِعِهِ لِأَنَّهُ مِنْ فِعْلِ الْيَهُودِ
Translation: “It is disliked to circumcise on the day of birth or the seventh day because that is the way of the Jews”
Reference: Qawaneen al-Fiqhiyyah, p. 325