GATE

First thing you need to understand is that GATE is not exam to get job, it for pursue master or doctoral programme for IIT, NIT, IIIT, CFTI. Clearing GATE is mandatory to get admission in these colleges to pursue M.Tech or Ph.D. Also some PSU recruit engineers at executive level E1 in their company on basis of GATE score and some conducts their own exam, to get job in psu, you need to achieve good rank in GATE
Now to get job in PSU, the age limit depends on in which category you come like general, OBC SC, ST PwD, Ex - servicemen
If you are from General or OBC category, then you will not get job in PSU after 32-33 year age, but if you are SC, ST you may get chance to get job through GATE in PSU
If you PwD, ex servicemen and your GATE score is good, you will get job in PSU.

If you want to get into research programme M.Sc, then I think a rank of up to 200 will be fine, but there will be a detailed technical interview. For the course programme (ME), a rank of 30 may or may not get you a seat. A rank of under 10 definitely will, this is generally applicable for all the different streams of GATE through which the Aerospace programme at IISc admits students. The course programme is fairly intensive with 15 courses and A.M.E. Project. My friends used to stay very busy with so much coursework. The research programme has 1 to 1.5 years of research involved and 1-2 publications are expected, course requirement is minimal and only 4 courses are required. The M.Sc. Programme is designed to help the faculty to have students do their research, so it is entirely in their hands to let you graduate, just like in a Ph.D. The M.Sc. could take at least 2.5 years in most cases. Placements vary greatly from year to year. Companies that visit are Airbus, GE, Rolls Royce, Eaton, GKN aerospace, Timetooth etc. It might happen that a student with a good GPA also might have to apply off campus. Some companies don't have openings for M.Sc. Students.