It's simply a ballpark estimate so that a recruiter can get a feel for whether a candidate would be suitable.  It's not an absolute measure, nor 100% accurate predictor of capability.  Would you recuit somebody with "10 years of BA experience" if all they've done is Use Cases for example ? That's the idea of the interview - it allows greater detail of experience to be elicited and validated.

Sometimes the 'x' years experience requirement is simply a best guess filter (bit like specifying that someone should have a 2.1 degree, instead of just a degree).

As with all recruitment, a person's qualifications and experience are a guide only as to their suitability.  It's only after a period in the role that you'll know whether they're really the right person (and it's a bitl late then!).

Thank you for reply!

Another thing in job description is experience related to industry.

e.g. three years in health care etc.

and I can tell you they decline BA without health care experience. It is ridiculous!

The same as smbd is looking for driver for Chevy and decline candidate based on info that drive used Corolla and Civic only...