I made the mistake of providing my date of birth as being 1/1/1900 on multiple websites, and have been receiving marketing material from the AARP in the mail for many years.

My "birthdate" is the same as yours. It was fine when I started using it in the late 90s, but has become increasingly awkward over the past few years - lots of sites seem to assume a maximum age of 120.

If I ever turn uBO off, the ads I get are mostly for funeral plans or incontinence products, with a smattering of "126 year old mom lost 30 lbs of belly fat - click to see how!" (yeah, decomposition's a bitch...)

That's not a mistake. You'd be getting spam marketing anyway, why not make sure it's something obvious? I always pick the oldest possible age when asked, just to mess with their data, because they shouldn't fucking care.

Don't limit, notify.

Has worked for TV (and movies to an extent, though theaters do limit somewhat, must have been some litigation around that...) pretty much forever.