what should i make of this?

it's a female coworkers last day at work today. she's only worked here for a few months. i am 22 years older than her. she asked me if we can exchange phone numbers and we did. she then tells me to call her the next time i go out for drinks. i just think it's a little odd that she'd do that because of our age gap whether it's just a friendly night out or otherwise. had i been her age i would have asked her out right then and there....what do you think?