You see, when men experience it, it happen spontaneusly from early age without the need of any external trigger which can happen from age 5 or even less. However as hormones increases during their physical development, this frequent and involuntary thing become more noticeable during puberty, which is roughly age 9 to 15. So its almost impossible for a men to remember
Do you remember your first? -Or do you not care about things like that?