Which one would you prefer to write, say, and live under? I don’t know where these people are living, but I’ve only met one male
Casey (over a pretty nice amount of female bearers); I’m in the Southeastern, USA. Perhaps, it was more common among men pre-2000, but it isn’t the case now. I also think that
Jennifer is a beautiful name, because while not as trendy for teens (though, I personally know 3, who are 18 years old), it’s very flexible and known. I’d say, you’d be good with choosing either name; I wish you luck with this process!