Hello Aspirant,

Yes, you can join competitive exam coaching classes from 11th. If you wish to prepare for UPSC, then you may join any coaching classes. Mist of the students now a days, join coaching classes compulsorily for the studying about UPSC.

But, remember, it must hamper and come between your daily study schedule mostly. If it comes, then your 11th and 12th  would not be good and you could end up getting low grades in your 12th examination.

You can also start preparing for UPSC after 12th, there's no compulsion that you have to start studying and preparing for UPSC after 11th. I am just saying this because, you will only get a good college for graduation if your 12th grades would be good.

But, if you can handle both, 11th std studies and going to coaching classes then it's fine and OK.

There are various platforms available from where you can study and gain knowledge about this competitive exam.

Hope that helps. Good luck