Hello,
There is no age limit for appearing for GATE exam. You can appear for GATE exam at any point of time to pursue a Master's degree or P.hd from a reputed institute. Depending on your rank and score in GATE, you can get a seat in IITs, NITs and other institutions for your Master's or P.hd.
As you have had a long break from your studies after your bachelor's degree, you really need to thoroughly revise all your concepts and work hard for GATE. Please visit this link to download the syllabus for GATE exam according to your branch. https://www.google.com/url?sa=t&source=web&rct=j&url=https://engineering.careers360.com/articles/gate-syllabus/amp&ved=2ahUKEwjixLf-z7XqAhVGbysKHb-zCzsQFjAAegQIAhAB&usg=AOvVaw1I0K3lgGG4PUPsKLwz9bSf&ampcf=1

Also , please note that for getting job into PSUs through GATE exam, the eligible age is 25- 28 years. ST/SC/OBC students get a relaxation of 3-5 years.
As you have passed your bachelor's in 2006 so you won't be eligible for getting jobs at PSUs.

For more details about GATE exam please visit this link https://engineering.careers360.com/exams/gate

Hope it helps

Graduate Aptitude Test in Engineering

Application | Eligibility | Exam Pattern | Admit Card | Preparation Tips | Books | Question Paper | Accepting Colleges

Get Updates Brochure