Hello aspirant,

If you are serious about clearing the UPSC exams than I would say you start preparing from the day 1 itself, that means you start preparing along with your graduation, once you are above 21 years of age you will be eligible to give UPSC exams, so please try as soon as possible. I wont suggest you personally to have just one year of coaching as its not enough to crack the exam. It is highly prestigious and tough exam and you will need good amount of time to study all the subjects.

I hope this helps.