Is it permissible to offer the 'Isha prayer immediately after Maghrib for a 12.5-year-old son due to his early waking for Fajr prayer and his late study schedule that conflicts with the 'Isha prayer time?

The basic principle is that each prayer should be performed at its specified time, based on the Almighty's saying: (Indeed, prayer has been decreed upon the believers a timed ordinance). Combining two prayers is not permissible except for a valid excuse, such as travel, rain, or hardship. If the time for the 'Isha prayer becomes very late and the time for Fajr approaches, making it difficult to perform the 'Isha prayer within its time, it is permissible to combine it with Maghrib by performing them earlier (jama' taqdeem).

Sheikh Ibn 'Uthaymeen was asked about lands where the red twilight (the time for 'Isha) delays significantly, and he replied: 1. If the twilight does not disappear until Fajr begins, or it disappears at a time that is insufficient for performing the 'Isha prayer, then these people should estimate the time for 'Isha based on the nearest countries to them, or based on Makkah's time. 2. If the twilight disappears long before Fajr, with sufficient time to perform the 'Isha prayer, then they must wait. However, if waiting becomes difficult for them, it is permissible for them to combine 'Isha with Maghrib by performing them earlier (jama' taqdeem) to remove hardship and difficulty, based on the Almighty's sayings: (Allah intends for you ease and does not intend for you hardship) and (and has not placed upon you in religion any difficulty). This is also supported by the action of the Prophet (peace be upon him) who combined two prayers in Madinah without fear or rain, "intending not to cause hardship for his nation."