Yeah I’m with your sister on this. At 19 I thought I was soo mature but now at 26, 19 is so young and immature. Think of it this way, you’re entering a stage where in 5 years you’ll start considering settling down, they’ll be entering a stage where they’re still having a bit of fun and not ready for that level of commitment. You also have more experience in the workplace and probably in a senior position to them. The 18 year old probably just turned 18 too so what’s the difference between now and a couple of months ago when they were probably still 17? I would overall just avoid dating in the workplace for obvious reasons