Toss a coin. Or ask your character. Or choose whichever is harder for you to write.
It’s your story. It’s your choice. If you’re undecided about gender, sketch out your character as in depth as you can and see if an answer presents itself. If not, pick one. You may change it in later drafts anyway.
Or they could be both or neither
Inspiration isn’t what gets your book written. Discipline is.
Inspiration is fickle: it shows up when you least expect it, all sexy and exhilarating and reminding you why you put your butt in that chair and turned off Tumblr and forced yourself to trudge through the valley of no-good, very-bad first drafts. Enjoy that inspiration while it’s there. Enjoy it thoroughly because it is rare and precious.
Just don’t expect it to show up every day. The only thing that needs to show up every day is yourself—and your determination to see this through to the end.