Thanks for A2A!
I will try to answer this question.
In the year 2018, life expectancy in India was around 69 years. Considering your present age of 40 years, you are going to live approximately 30 more years. That means you’re gonna live with the tag of your speciality branch for roughly 27 more years. That is a hell lot of time to excel in the speciality you want to do.
Let’s discuss the other side of it. India is a very competitive country. Considering that you’re going to start your PG at the age of 40, most of your colleague will be approximately half of your age (approximately 24- 25 years). This might create an unhealthy environment for you to work. Moreover, residency is a demanding course, that will exhaust you physically, mentally and financially. Considering your age I assume that you must be married with children, this will put an extra burden to your family as well. Three years of limited time for your wife and children plus no stipend (Pvt college) and tuition fees (Pvt college).
Evaluate all the pros and cons before enrolling for the PG course.