Do IIT'S are allowed BTech Year Back students in Mtech admissions ? With good gate score and also 6.5 cpi for 7th sem? Please tell me allow?

The minimum eligibility criteria is that you must have passed your B.Tech with at least 60% marks or 6.75 CGPA (though it varies in different IITs , it may be 6 or 6.5 sometimes). It doesn't matter if you had backlogs or yearbacks.
Some of the IITs select candidates as 80% of the GATE score along with 20% B.Tech marks. So you just need to have the prescribed marks for getting admission.