National Institute of Fashion Technology, Delhi

The eligibility criteria of M.Des. from NIFT is given below.
Educational Qualification for Masters Programme in Design :- Undergraduate Degree in any discipline from any Institute /University recognized by law in India
or
Undergraduate Diploma of minimum three years duration from NIFT / NID.
So from above, If you have completed the three year of diploma from NIFT/NID. than can be eligible for M.Des course but can not get admission in final year of M.Des course.
Further admissions in M.Des courses are based on an entrance test conducted by NIFT.
The eligibility criteria of B.Des is 10+2 or 3 or 4-years diploma recognized by AICTE or a State Board of
Technical Education. So B.Des course is required 3-4 years of Engineering diploma courses of AICTE/State board of technical education. Hence you are not eligible for this course if not completed 10+2. The admissions in asked courses are also done on the basis of NIFT entrance exam.

B.Des eligibility criteria of NIFT is given below.
1. Qualifying Age: Maximum age should be 23 years as on 1st October, 2019. The upper age limit may be relaxed by a period of 5 (five) years for candidates of Scheduled Caste/Scheduled Tribe/ Person with Disability (PWD) categories.
2. Educational qualification for Bachelor of Design (B.Des) Programmes (Fashion Design / Leather Design / Accessory Design / Textile Design / Knitwear Design / Fashion Communication) : The +2 level examination in the 10+2 pattern of examination of any recognized Central/State Board of Secondary Examination, such as Central Board of Secondary Education / State Board New Delhi, and Council for Indian School of Certificate Examination, New Delhi.
So from above age criteria is very important. The Gap of 5 years after 12th is not a big issue because you have completed your graduation during this period. So you can be eligible if meeting the age criteria as above.
Further you are also eligible for M.Des course of NIFT because there is no age restriction for M.Des course. While the eligibility criteria is Graduation in any discipline. The admission in M.Des are also done through NIFT entrance exam.