I am almost certain there is something else going on here other than your age. In fact, I've never once been asked my age in an interview, and I'm a couple of years into my second career doing this after I retired from my first.
But my point was that there are market segments where age literally doesn't matter one bit.
I'm retired from my first career and writing code every day for a second career, well over 40. I've interviewed for five jobs in that time frame and been offered every single one -- and I don't interview for management roles because I hate managing (it's what I did for 20+ years in the Navy).
In my experience it's not about age. There are jobs, one just has to find what fits them.
1.) Most people can do math. Unless you're also going to be evasive more or less throughout your resume about how long you were in roles and the like, people are going to figure out your rough age/general seniority pretty easily. And at some point it looks evasive. Maybe you're trying to hide some big gap that exists for some reason.
2.) But let's say you do scrub your resume and no one calls you on it. You're presumably going to have an in-person interview at some point and they'll, again, figure out your approximate age pretty quickly unless maybe you're exceptionally young looking.
3.) All this assumes that no one actually knows you when, in my personal experience, every job I've taken since grad school was through someone I knew.
I rarely apply for a job cold. I've nearly always had some point of networking somewhere.
Even for the job I have now, for which I did just send in a resumé and an application cold, I have some very specific key words on my resumé that the hiring manager recognized and then started asking if I knew person x and person y and so on and we discovered that we have a bunch of prior colleagues in common, which also made me extremely useful to the organization in ways they don't advertise (I already knew this going into the interview, as I did my research).
Finding a job is very much about market segment, branding, and networking. If you're "just another web dev" and have no other meaningful skills and no friends, then maybe finding work after 40 is hard -- I wouldn't really know. If you're a C++ guru with an MS, an embedded dev, a specwar comms tech, etc, you get really valuable to some people because you've got such a broad set of experiences, and they don't give a rat's ass how old you are as long as you can still hobble in to work some days.
And sometimes they'll hire you for your network as well, which isn't all bad either.
2) Getting an interview is all a resume is good for in the first place. Now they've invested their time in you and you have a chance to sell yourself.
3) Same here, but even people who "know" me professionally don't necessarily know my age. I certainly don't know all of their ages! Plus if they know you, they already have an incentive to care less about your age.
Not true, in German speaking countries having your photo, birthday and work/graduation dates in your resume is basically mandatory, especially when applying at big established companies.
Omitting them could have your resume disqualified as HR might think you're trying to hide something or that you haven't bothered to do it right.