Hello Aspirant,
See as per your Date of Birth your age in 2024 would be 21 years do from 2024 if you pass class 12th then you can appear for UPSC CSE examination because the age limit for UPSC CSE exam is 21 year to 32 year with following age relaxation as per the reservation criteria of UPSC :-
>>>> OBC - 3 years
>>>> SC/ ST - 5 years
>>>> Defense Services Personnel, who got disabled during operations during hostilities with any foreign country or in a disturbed area and released as a consequence - 3 years
>>>> Ex-servicemen including Commissioned Officers (CO) and ECOs/ SSCOs who will render at least five years Military Service as of August 1, 2021, and have been released - 5 years
ECOs/SSCOs who have completed an initial period of assignment of five years of Military Service as of 1st August 2021 - 5 years
>>>> In the following cases: blindness and low vision, deaf and hard of hearing, locomotor disability including acid attack, cerebral palsy, leprosy cured, dwarfism, victims and muscular dystrophy, intellectual disability, autism, specific learning disability and mental illness - 10 years
>>>> Candidates ordinarily domiciled in the State of Jammu & Kashmir from January 1, 1981, to December 31, 1989. - 5 years
>>>> So as per the age criteria you will be eligible for UPSC IAS exam 2024 because the candidate should have crossed age of minimum 21 years on the August 1st of examination year.

You can check out the detailed eligibility criteria for UPSC IAS from the link given below :-
https://competition.careers360.com/articles/upsc-ias-eligibility-criteria

I hope this information helps you.
Good Luck!!