If you want to answer "because that's exclusionary", have you considered that maybe, just maybe, there's a reason women have those preferences? Have you also considered that maybe, just maybe, those reasons could be valid?
It doesnt matter what moral justification exists for preferences. What matters are results, which in the end exclude a lot of men, and leave women competing for smaller number of men, where unless polygamy happens, women end up lonely as well. And LGBt is like 1% of society, so unless women "turn gay", having standards which excludes 10 to 20% of straight men pretty much guarantees that 20% of women must be lonely, turn gay, or be in polygamy (which isnt common enough).
And the standards arent exactly morally justified, when you understand what those standards are.
It exposes a deeper problem, apparently that of women in most cases dating men older than themselves, essentially forcing a lot of men their age to date younger than themselves or be alone.
Women in most cases seek older partners. this means a man at age 18 fails to find a girlfriend of his age, because all the girls his age prefer men over 19 or 20. this essentially forces an 18 year old to either be alone or date someone under 18.
the math behind this is that if only 40% of 18 year old girls choose men over 19, it means 40% of 18 year old guys face a choice of being lonely or date women under 18.
One could say that men can also date older women, but that is rarely preference in men, and also, older women also happen to prefer men older than themselves.
Women's standards of "dating 2 to 4 years older than themselves", which seem to be very common, isnt any benefit, because it means men their age cant date them in most cases.
While men have no problem with dating their own age, women seem to mostly prefer older men.
If you think that standard is morally justified, then tell me who is an 18 year old straight guy supposed to date when such standard is applied?