I think you should skate regular stance..
Cause thats you're natural stance ,and thats what you feel comfortable with right.. Its only normal thats what you should stick to..
And no you're dominate foot usually is the leading foot which is the one you place on the board while pushing while you're back foot pushes. etc.So you are on the right track don't worry ..
I'm right handed and my right foot is my dominate foot and i skate goofy.. Though me skating all these years has made me ambidexterous. I can skate anyway and it looks natural. Etc.
I think its cool for a girl to choose to skate no matter what age. But the more mature the better , i give them props.. I like when i see skater girl outhere even if they just use the board to cruise around..
If you are planing to pick up skateboarding be ready you will get a good work out gain strong legs and aquire really good balance and stamina.
Its 100% about your preference thats the awesome thing about skating its purely wjat feels natural that will determine how good you get. Nobody can truly teach you how to skate. Some people are aggressive skaters and flick the board as hard as they can to do a kickflip and some just do it calmly but it works for both. As far as skating goofy or reg I skate goofy and I'm right hand dominant but my buddy skates goofy and he is left hand dom. Its all on what feels good. Take skating and model into your style.the fact that your 20 doesn't matter its never too late. And we need more chicks in the skate world. Mix it up some lol. If you have any specific questions hmu I've been skating since I was 9 and I just turned 20. Have fun anyhow :p
Really it's whichever feels the best. If you're more comfortable goofy, skate goofy or, if you like regular, do it regular. I used to skate and and always skated regular even though I was left handed. Also I think if you like skating then you should skate.
It doesn't matter. Push mongo if you prefer too.