Honestly, you won’t be able to get a seat at AIIMS if you start preparing now. You required an AIR within 100 in NEET, one of the most difficult exams for UG in India.
However, if you have studied for AIIMS previously and had taken a drop year then there are still chances. Give it your all and start studying passionately.
In most cases, however; it’s difficult to start from the beginning and get a seat unless you are a genius who gets 4-5 hours of sleep only and employs the best resources.
I have seen various people get admission with just a preparation of 4 months. Miracles do happen, all you need to do is believe in yourself and start preparing right away without wasting a single minute here.