It is someone I have known for 30 years and I am just being nosey curious as to when they were born. They have been married for approximately 55 years. No idea where they were married other than an assumption it was near where they live now.
Assuming I had a good reason for doing it myself rather than just asking I would start by doing an Ancestry marriage search for [her first name] [blank surname] with spouse's surname [their married surname], and hoping that there weren't too many results. If you know husband's first name that would help to narrow it down.
That will give you one or more possibilities with maiden surnames, then you can do a birth search for [her first name] [her (potential) maiden surname] and a very vague span of dates (e.g. you'd expect her to have been born somewhere between 1909 and 1939).
I'm not sure how much you can dig up about living people - i was sort of assuming you were looking for family hostory, and the individuals would all be dead - that makes a difference in what info is available ot the public.
If it's an unusual first/last name combination it's easy enough to do for anyone born before 2005, if births and marriages took place in England and Wales (or in Scotland, although the only register search I know for Scotland charges by the page for results so it works out pretty expensive to do speculative searches so I'd have to want to know really badly).