It's mostly known as a girl's name where I come from (I grew up in New Zealand and am in my 30s - and female). But here in the UK, people do, amusingly, expect me to be tall, male and able to cook.
Having said that, it wasn't widely known when I was growing up, and I hated it because I constantly had to enunciate it and contend with people calling me Angie/Ashley/Anneliese (go figure the last one).
I found that it was better-known in Australia (as a girls' name), thanks to the quasi-notorious Ainslie Gotto (some grand old men of politics attributed her influence on the PM of the day to her being hot stuff rather than her grey matter - but that was all before my time!)
At least people here in the UK are familiar with the name - I just have to say 'just like Ainsley H but different spelling and I'm a girl' and they usually go 'oh right'.
As for the spelling, I think the first name spelling variants are along regional (Scots vs English) rather than gender lines.
Oh, and I have met three other Ainsley/Ainslies (all female). One was nice, two were bitches! :o