If there was a guarantee age and experience provided a better player, then great but it doesn't. Our whole transfer strategy has been to sign younger players (20-25), with a few exceptions and it's given us some players who have turned into long term world class trusted players for the next 5-10 years in some cases like De Bruyne, Sterling, Laporte, Ederson etc.Fair enough, but let's be honest, if going for a defender like Koulibaly goes wrong as well then we're just cursed in buying defenders who either turn shite or are injury prone.
All these fancy names that aren't on market like Upamecano or Koundé are too young and have had 1 or 2 good seasons with little experience, signing them could be an equal mess (do get value for them moving on, but a failure would be useless and their value recouped would mean nothing in the bigger picture). There has to come a time where the club changes policy to sign an experienced player who would not only help the backline but potentially be a leader. We have a fairly young squad in general, barely any players who's age is a big concern. Sometimes experience like this is necessary, I just hope, like most that if he comes he is great and more.
It boils down to right player at the right price, if the club believe Koulibaly represents good value for money, perfect. I don't but who cares what I think.