Age discrimination will probably always be a sad part of the hiring process as long as humans are in control. But there are some things you can do with your resume to limit your risk of rejection:
Limit the number of years that you summarize in your profile
Don't broadcast the fact that you have 25, 30, even 40 years' experience in the summary at the top of your resume (or your cover letter, LinkedIn profile, etc.). It's often one of the first things the reader sees, and if they're looking for someone who is at an earlier stage of their career, they'll move right along without giving yours a second look. You want your resume to actually be read, not discarded with little more than a glance.
It's fine to be proud of your extensive work history - you should be - but take a more strategic approach to summarizing it for recruiters.
Say you have spent 30 years in retail, 25 of those in management positions, and 10 of those as a district manager. Instead of boasting about 30 years in retail or even 25 years in retail management, focus on your 10 years as a district manager. Here's an example:
Award-winning retail district manager with 10 years' experience in progressive multi-unit leadership positions.
If someone is looking for a district manager, or even a top candidate for a regional position, they'll likely want to continue reading your resume. You haven't given them the immediate impression that you're close to retirement by bragging about 25 or 30 years' experience.
Focus your resume on the last 10-15 years
Remember, a resume is a marketing tool designed to help you get interviews. It's not necessarily a complete listing of everything you've ever done.
Recruiters are primarily interested in what you've done lately, not what you did 25 or 30 years ago when the world was a very different one than it is today. So focus your resume on what you've done in the last 10-15 years - that time period should take up probably 80% of the space on your resume.
If you have experience from the previous 10-year period that you believe is really important to include (ie. 15-25 years ago), briefly mention it at the bottom. Don't include dates for that employment, but also don't make it seem obvious that you're leaving out the dates. Try something like this:
Previous retail leadership experience as a store manager for Sears Holdings, PetSmart, and Barnes & Noble. Managed a flagship store for PetSmart. Awarded "Store Manager of the Year" with Sears.
Since this previous experience isn't presented in the same structured format as your more recent work history, it comes across as more acceptable that dates are not included. It also doesn't take up much space, leaving room for your more recent jobs and accomplishments.
Job searching is all about marketing yourself, and in marketing you want to carefully consider and control the message you put out there. It's important that you never lie - don't pretend to be 45 if you're really 63 - but at the same time don't make it easy for recruiters to dismiss you. The goal is to get to the interview, where you can WOW them in person.
I wish you all the best in your job search!