بسم الله الرحمن الرحيم
The feeling and longing of marriage comes in the mind of man itself. If your doctor brother who has now turned 42 years of age is ready for marriage then some suitable match should be found out for him. Marriage may also be done at the age of 42 as well. If he is not willing to marry then he may be motivated by his friends and in case he feels some hindrance then it should be removed. Pray Allah to get a suitable match. Your brother should recite Ya Jame (يا جامع) eleven tasbih i.e. 1100 times and moreover the family members may also read Ya Latif Ya Wadud (يا لطيف يا ودود) 1111 times with durood before and after and supplicate Allah. However, if some proposal comes then do istikharah along with consultation and then finalize the proposal, in-shaAllah, it shall have goodness and blessings.
However, if your elder brother is not ready for marriage then there is no use to force him for marriage.
Allah knows Best!
Darul Uloom Deoband
This answer was collected from the official ifta website of Darul Uloom Deoband in India.