At what point is someone considered too old (in terms of experience) for an Assistant Professor position? I competed for an Assist. Prof. in Greece with someone with 12+ years experience since PhD. Suffice it to say that it did not turn out well for me (4 years of experience) or other interviewees for that matter, even though many of us had the better* research output in terms of quality, ranked venues, and achievements (3rd party grants and so on), but clearly not as many citations as we do not exist long enough in the field.
It also did not help that the committee favorite had their BSc, MSc, and PhD in that same university, and 12+ of postdoc in a partner lab in the vicinity.
But, anyway, I asked the committee the following question, which I also pose here: At which point (if there is such a point) is someone considered too old (in terms of experience) for an Assist. Prof. position?
They told me that the favorite had a higher citation count, so even if they were 60 years in the field they would still rank them first because of that. In my opinion, even though that might well be legal, it does not seem very ethical to me.
I am under the impression that an Assist. Prof. position is an entry level position where you are supposed to form your own lab, attract early-career grants to help you with that (which have experience-age restrictions), and work towards becoming a professor.
*As an example, I will simply say that the position was on AI with a focus on Knowledge Representation and Reasoning, and the committee favorite had 0 articles in IJCAI, AAAI, KR, AIJ, or JAIR, whereas I had 6.
No sane committee is ever going to turn down a candidate solely for being 'too experienced', and it is rarely meaningful to reduce someone's CV and accumulated experience to just a few numbers. However, this comes with some qualifications:

If someone is reaching career milestones (e.g. first Asst. Prof. job) much later than the norm, a committee might question why, and whether this is a sign that future development will be slow.
If someone is applying for a job that is 'too junior' for them, committees might be concerned that either (i) they're not really a serious applicant, or (ii) that they'll quit as soon as something better comes along.
By definition, if someone has more experience, then the committee has more information on which to base a decision. Junior candidates often have to be assessed in terms of 'potential for success' rather than 'evidence of success'. This can count for or against the more experienced applicant: some committees may prefer to gamble on a rising star, others may prefer the security of an established candidate.
Hiring decisions (just as everything else) are influenced by many external factors. Everything from financial considerations (experienced candidate may cost more) through to government policy (how candidate's metrics would influence the university's ranking and hence income) may help sway a decision for or against a particular candidate.