IIT

No, the percentage doesn't affect IIT rank but you have to score a minimum of 75% (65% SC/ST) or should be in top 20 percentile of your respective board to be eligible to give the exam.

Yes, you are eligible, here's the eligibility:
12th Class/Equivalent Exam Passed Out Candidates in 2016/2017.
12th Class/Equivalent Exam Appearing Candidates in 2018.
Diploma holders who have already passed or are in their final year of their Degree.

Bachelor's degree in any discipline of engineering technology with first class or its equivalent or a Master's degree with first class or equivalent in any discipline from a recognized institution or university.

Hello Goutham,
I am attaching a link that will give you all the required information.
https://www.shiksha.com/engineering/colleges/m-tech-aeronautical-engineering-colleges-india

Let me clear few things. To get admission in IIT, one must clear JEE Mains as well as JEE Advance with good ranking.
For NITs admission, you need not appear for JEE Advance. A good rank in Mains is enough.
Next comes OBC category. Unlike SC/ST or OBC, there are two categories further. Creamy layer and non-creamy layer. If your family income is up to Rs.5 lakhs, you are non-creamy layer. But, if it is above that, you will be treated as creamy layer and you will be treated as general category student.
And, you don't need to score a 90% marks in your class 12th boards. In fact, 70% marks is the eligibility criteria for JEE Mains.

Hello Ramasai,
For architecture courses, you need to clear JEE Mains paper 2 and JEE Advanced. To get admission into IITs for B. Arch courses, you need to clear an Architecture aptitude test (AAT) based on which you will be allotted seats.
However, JEE Mains paper 2 scores are being accepted by many reputed colleges.

Both are very different profiles and have good pay. And mind it, both require a lot of preparation and dedication. Aviation is the second after Bollywood in India in terms of Glamour. IIT engineering also has a very good pay.