Would the young man be sinful if he does not perform Hajj this year, despite his financial and physical ability, because his mother asked him to postpone Hajj until next year so she could go with him?

Scholars have differed on whether Hajj is obligatory immediately (على الفور) or with delay (على التراخي). The view of the majority is that it is immediately obligatory, and this is the strongest in terms of evidence and the most cautious for the religion. One who delays it despite being able to perform it commits a sin. The majority cite as evidence the Almighty's saying: "And Hajj (pilgrimage to Makkah) to the House (Ka'bah) is a duty that mankind owes to Allah, those who can afford the expenses (for one's conveyance and provision for himself and his family, etc.)" and His saying: "And complete the Hajj and 'Umrah for Allah." The command here implies immediacy. They also cite the Prophet's (peace be upon him) saying: "Whoever intends to perform Hajj, let him hasten." Therefore, you must hasten to perform Hajj and apologize to your mother, explaining to her the religious ruling on the matter.