As per the UPSC CSE examination rules, the student need to be atleast 21 years of age on or before 1st August of the appearing year. Now you are getting 21 years on 23Sept,2023. So you are not eligible for the UPSC CSE 2023 as you are not turning 21 on or before 1st August,2023. Your first attempt of UPSC will be considered from the UPSC CSE 2024. The maximum age limit for the UPSC CSE is 32 years.

For more information regarding the UPSC preparation tips consider the link below:

https://competition.careers360.com/articles/how-prepare-for-upsc-ias

I hope this helps. Wish you a great eve!