Pikachu boy or girl ?

It doesn’t matter the gender, it is strange that all the 500+ CP Pikachu are all f male

Which you personally prefer. For the vast majority of Pokemon, gender makes no difference to their capabilities. A few, most notably Wobuffet, have slight visual differences.

However, it's worth bearing in mind that Gen 4 introduces a few gender-specific evolutions:
Burmy - females evolve to Wormadam and males to Mothim
Combee - only females can evolve to Vespiquen
Snorunt - females can evolve to Froslass
Ralts/Kirlia - males can evolve to Gallade

There's also Salandit in Gen 7, but that's a long way off.