NATA

Conducted by the Council of Architecture, NATA (National Aptitude Test in Architecture) is a national level common Aptitude Test in Architecture. The exam measures the applicants' drawing and observation skills, sense of proportion, aesthetic sensitivity and critical thinking ability, that have been acquired over a long period of time, and that are related to Architecture.
A single window exam, NATA is used for admissions to first year of 5 year B.Arch Degree Course at all recognized Institutions only in India. NATA 2018 exam dates will be declared soon. In 2017, the exam was held offline on a single day on April 16.

Please refer to the link provided below for details regarding cut-offs for students in the reserved category to gain admission into NID.
https://www.shiksha.com/design/fashion-design/articles/nid-admissions-2016-cut-off-scores-blogId-12369

It is never necessary to do anything. However, if you feel you are lagging behind with your studies and preparation for NATA, you could definitely opt for coaching. Go through the syllabus, and exam pattern to see if you will be able to cope with preparation on your own. If you feel you can, then do it. If you think you need external help search for some of the better coaching centers to help you out. Good Luck!!

Minimum Eligibility to Apply
12th 75%
Additional Details
Mandatory Subjects : Chemistry, Mathematics, Physics
State wise top 20 percentile holder in class 12 exam are eligible to apply.
There are no B.Arch courses available in this college, only B.Tech courses. Above eligibility is for B.Arch courses.

Please refer to the link for complete details: http://www.nata.in/.

NATA 2018 results have yet not been declared. You can await notifications when application begin in February next year.
https://www.shiksha.com/architecture-planning/exams/nata/dates

There is no lower age limit to take NATA 2018. Without any limitation, you can give NATA exam.

Eligibility for B.Arch:
Candidates should have passed 12th standard or equivalent examination with a minimum aggregate of 50% marks with Mathematics and English as subjects of study. 10+3 Diploma (any stream) recognized by Central/ State Governments with 50% aggregate marks.

Some of the popular books for preparation for NATA entrance exam are as follows:
A complete Self Study Guide for B.Arch. Entrance Examination 2018 By P K Mishra
NATA Guide to B. ARCH Entrance Examination with solved papers 2013 -16 By GKP
Steps to Architecture NATA and JEE Mains Entrance Exam Guide By R Gupta
NATA & B.Arch Question Bank By Ar. Shadan Usmani

Please use the link provided below for details regarding admissions in Manipal University, Faculty of Architecture for B.Arch. You should be able to download their brochure which contains details regarding NATA eligibility and admission process to secure a seat in Manipal for B.Arch.
https://www.shiksha.com/architecture-planning/course/b-arch-manipal-university-faculty-of-architecture-192900