I think that in India research institutes will never take a faculty candidate who is over 35. Is it so all over the world?
I am asking this question from the point of view of if someone starts their PhD. at the age of 27 then its unlikely they will be faculty candidates till they are 40.
Age discrimination is explicitly illegal in the US. (I believe the same is true in Canada and most European countries.) Even as the chair of my department's recruiting committee, I am forbidden to ask the age of any applicant.
If you're worried, just don't put your date of birth on your CV. But this really is a non-issue.
(This started out as a comment on JeffE's answer, but became too long, and I don't want to clutter his post.)
This is a gross simplification, but what hiring committees care about is your future research potential. In the absence of a crystal ball, they have to extrapolate from your previous achievements: The more in less time, the better. For this, your actual age is irrelevant - it is only important how long you have been an active independent researcher, which usually starts after your PhD. (This also touches on the point @user11192 made.)
Tl;dr: It's not age, but age minus time of PhD, divided by number of publications (and grant money squared).
In some countries academic studies will only start at an age of ~22 due to factors such as military/civil service etc. which may yield:
22 + BSc (3 years) + MSc (2 years) + PhD (4-5 years) + (Postdoc 3-4 years) = 35 to 37
In this case 35 would be considered a typical, or even relatively young age for a candidate.
short answer, no. There are 40+ year old new professors who will get tenure after starting work at a new school in the US. There are 35 year old first time science majors landing jobs because of their passion and I recently met a 55 year old who just completed an EET degree who landed a position at a decent firm with a good wage although he has a math phd as well from 30 years ago. It is mainly cultures where age discrimination is the disgusting norm and Google. India may be the worst country on earth in terms of age discrimination and bribery. There are job postings I saw (just out of curiossity from an article on this very subject) explicitly asking for no one over 26 where in the US those positions would say 10+ years of experience or a phd (experience preferred). If immigration is a possibility then it may be the best route. Some other countries have age discrimination issues as well but, generally with the exception of India, countries that were part of the British empire with its legal system tend to be more lenient. You have options. Age discrimination hurts everyone. Experienced professionals tend to demand less, are less restless, and require less training. Maybe a cultural shift is in order?
This answer stems from a few comments I made to a related question.
Are old (>35) faculty candidates discriminated against all over the world?
I can't speak to the worldwide aspect of the question. What follows will be specifically tailored based on my tenure-track job hunting experience in the U.S., although it may be applicable in other parts of the world.
As pointed out in another answer, it is illegal to discriminate on the basis of age in the United States.
However, I think the more interesting question to ask/answer is: Even though it is illegal to discriminate against someone due to their age, does that mean that age plays no role whatsoever in tenure-track faculty hiring decisions?
Sorry to get your hopes up: I don't have so much a concrete answer to this question; however, I offer an example of something an "older" candidate may face when seeking a tenure-track faculty position.
Being an "older" candidate myself, I noticed on my unsuccessful interviews earlier this year that I seemed to get along just fine with tenured faculty; however, there was clearly some tension between myself and the "younger" tenure-track faculty at several places that I interviewed. If age did indeed play a role in this perceived tension, one may easily see why younger candidates would have an advantage. Furthermore, since most tenure-track candidates are from the same age group, the fact that an "older" candidate doesn't gel with his peers of the same academic rank for "some reason" makes you stick out like a sore thumb.
Ultimately, I think that if age does play a discriminatory role in faculty hiring decisions, it may be that it is an indirect discrimination. That is, in a direct sense, nobody cares about your age or have been trained to think that way. But if you don't have similar personality characteristics of those tenure-track faculty already in the institution's employ, then there is still some likelihood that you will be marked as a bad fit for the job. How high that likelihood is I cannot say.
It is the ratio of your accomplishments to age that matters. Generally accomplishments saturate with age and hence it appears that there is an age discrimination. I am sure a 50 year old Nobel Laurette will be hired directly as Professor at many Universities.
My university is planning to hire >100 senior faculty. Presumably none of those people will be young. The idea is to buy the university a world-class reputation. I think other universities that have money and a desire to increase their rankings use a similar strategy. Poorer universities hire younger faculty with an expectation they can be paid less.
