The lower age limit for the UPSC CSE examination is 21 years of age. The age criteria also suggests that the student must turn 21 year of age on or before 1st August of the appearing year. So if you are thinking of appearing in the UPSC CSE 2025 then you need to be 21 years of age before 1st August, 2025. On 1st August, 2025 you will be 20 years 9 months 18 days of age. As a result, you aren't eligible for the USPC CSE 2025 but you are eligible for the examination from 2026 onwards.

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

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

I hope this helps. Wish you a great day!