hello Breandán
i'm here to awnser your questions.
no. with sure I belive that anyone can be able to draw. Draw is like music: you need a lot of treaning if you want to get in somewhere, even a genius as Da Vinci had to make many anatomy studies over his life.
so we, normal people, will have to make much more: you'll have to draw a lot, draw everyday, draw like this could be the last day of your life.
Practice it's the only solution if you want to get better, observe people walking on the street, observe real people is the second key to improve.
so, i'm 19 now and I've been drawing since I can remember, and I certainly afirm that drawing ability has nothing in about genes. for exemple my mother work at bank and my father is an engineer, and both don't draw very well.
then, your ability only depends of your will. ^_^
hope that I helped.