Obviously age bias is illegal, along with sexual orientation, race, religion, and so on. But it still exists. Your best bet is to apply to larger companies that are more closely scrutinized, where there can't be a whiff of bias, as opposed to smaller ones that are more likely to get away with it. Its hard to say without knowing what you do, but if you could take classes for hard to find skills in your field, you are much more marketable. Skills that are in high demand no matter how old you are, such as certain software that is relevant to your work. Don't put things on your resume that don't pertain to the job you're applying for, such as a stint where you were dog catcher or worked at Walmart. Cut your resume off at 20 years of past employment, but under that state, "Additional experience and references upon request". If you had a stint of unemployment, put what you did in that time to stay active, such as pursuing more education. You don't want to look like you were busy at nothing.
Code for age bias are things like, "looking for an up and comer", "2 to 5 years experience", etc. Don't waste your time.
Finally, don't wallpaper your resume all over town. Nothing is more aggravating for a recruiter than to hear you've done that, which precludes them from talking to their client company about you. If they have a good relationship with their client company, they can make a presentation, submit you directly and make sure you get noticed, rather than your resume going into a black hole. Pick one or two good ones that seem genuinely interested in you, and have good reputations. I don't do candidate marketing anymore, so one of my specialties is going after people that aren't actually looking to change positions. The main place I find people like that is LinkedIn. Last time I looked, I had 7,000+ first connections on there, and that's where I start looking first. Be sure to put in specific words that will pull your profile up in a search. Skills such as mechanical engineering, MRP, aseptic processing. Be specific. There's a million project managers out there for instance, and a recruiter is not going to search thru all those. They're going to narrow it down to project managers with specific experience.
Hope that helps.
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