My work colleagues said I was the asshole for this so I would like more opinions.

I asked out a girl that I’d been flirting with for a while at the gym. She’s a bit younger than I am (28 vs 23) and I could tell during the date that she was a bit insecure about this. 

It was a good date and when it was time to pay, she told me she’d cover both our tabs. I asked if she was sure and she said yes. So I let her pay.

It’s probably pertinent to mention that given our career fields and ages, I definitely make substantially more than she does, which is part of why my coworkers said I’m an asshole, on top of not paying when I asked her out. AITA?