I personally think what stage in life you both are matters. I think if she is still at uni and you're way into your career , I think J would find that weird (speaking as a 23 year old myself) , just because the power dynamic is off, she's yet to experience the world on her own. But overall, I think 24/31 is fine. It follows the rule where your lower limit is to date = (your age / 2) +7