hi anunay ,

the basic eligibility criteria to write CAT is , that the candidate should have completed his/her bachlour degree .

and talking about the preparation , you can start it any time . you will just have to plan before starting and then start accordingly . according to me 3rd year is the best time to start your preparation  . so start it write away with proper planning and preparation .

all the best

Hi. If you want to appear in CAT 2018, then you should start preparing now. The earlier you start, the better it is. And if you want to appear in CAT 2019, then also you can start preparing now and take on the course slowly.

Thank You!