Kostic is older. I mentioned that in an earlier post, so I am fully aware of it. However, he will cost less and by the time 3 years have elapsed, his book value will be almost zero.
I don't think he's WC, but he seems solid and robust (like Mandzukic on the wings back in the day), but we only need one winger like that and another winger who's explosive and exciting. Ideally, I'd go for someone like Gabriel Jesus or Gnabry, but unfortunately it doesn't seem we're interested or willing to take the risk?!