The company BYJUs was founded in 2011. So it haven't been that long, such that the workers reach there full base of retirement. Also the company don't mention any such things on the official website of there website or in there vacancies as posted in different job platforms. So saying anything conclusive isn't possible. Although I would say for most of the jobs in private sectors or the government sector the retirement age is around 60 years of old. Also for Content Writing, the need for experienced writers are always there. So even if you get retired, you will get different offers from other companies who will offer you to work in there company as your experience will matter.

I hope this might have given you some idea. Goodnight :-)