This is a typical amount of semen produced by a young male at this age especially when they are highly excited ,boys this age produce heavily and their bodies ready to make babies .
If this was a teen boy he probably just stroked his cock knowing he would cum before he was even inside this milf ,not uncommon,as I did more than a few times .
Something about the "one tit out" has always made my cock rock hard. If i see a huge tit lady pull both tits out it's a turn on obviously, but if she pulls JUST ONE tit out my cock is instantly throbbing. No idea why...