Look up the definition. It's not a completely objective thing really.

But generally it's ejaculating before or shortly after penetration or stimulation. Or to ejaculate before you want to. Or to ejaculate without your control. Or to ejaculate before you are able to please your partner.

So it's pretty subjective. By some definition, if a woman took 40 minutes to reach orgasm through penetration, than a man who came in 39 minutes would have premature ejaculation.

I generally follow, "ejaculation before or shortly after penetration or stimulation. And ejaculation without control."

It's still subjective as to what is control and what is "shortly after" though.