Former recruiter and current professional resume writer. As the other respondent said, the quick formula a recruiter might use to guess your birth year is "college graduation date - 22" or "date of first job - 22".
You should keep this fact in mind as you write a resume and decide which jobs to include, which jobs to perhaps delete, and whether you want to include your graduation date. It isn't necessary to include a graduation year or all of your jobs, so you can usually shave some years off your age "on paper" without being considered as deceptive.
Sometimes I'll add a line "Previous experience included..." to indicate that there is prior work experience, but I don't list the years.
Just to add to that, these are the rules I follow. Needless to say, I am 50+
1. Don't include graduation dates in your resume, just the University/School name and Major(s)
2. Truncate your resume to just slightly over the required years of experience. e.g., include past 12 years experience for a job which requires 10+ years
3. Keep your resume to under 3 pages (max). Nobody has the time to wade through an 8 page resume, even if you have worked on the most awesome projects at the start of your career
I am curious. If what you described is a standard technique people can use, what prevents the recruiters/talent acquisition to, by default, discard resumes/CVs without exact dates?
I assure you it is a standard practice, but why would recruiters discard resumes without exact dates 'by default'? Because the assumption is that those people are 'old'?
That may answer the question for you, but ageism is a legal concern and disqualifying candidates because they didn't tell you when they graduated isn't dissimilar to asking someone how old they are in a job interview and refusing to hire them if they don't.
As someone who hires, I like to see dates because I want someone that has a track history of sticking around for a while. I don’t want to waste effort on someone that has a history of changing jobs every year or two. Dates help show that.
When I started my career as a programmer it was a bad sign if people didn't stay 5 years at least at a company. But these days hardly anybody stays longer than 2 years unless they're being paid exceptionally well. So it's no longer a terrible sign if someone doesn't last more than 2 years. It can actually be a bad sign if you work at a big company for 10 years because you're probably out of date because you focused only on their tech stack .
I think resumes should be treated less as a report card and more of a brochure. Hiring managers have little time, so keeping it focused on relevant highlights and selling the candidate for that job are the entire point.
A 15 page menu isn't better than a 1 page menu... A spa advertising every stone in its parking lot doesn't make you think nice things about their mud baths...