Forming friendly acquaintances and friendships with people of different ages is completely natural. It certainly was regarded that way in the past. What has to be controlled is the manner in which such friends and acquaintances interact.
It is considered abnormal (by many people) if someone does not have a wide circle of friends (friendly acquaintances) their own age.
I do not think that's fair, but it is true, that in ordinary times it would be much easier for Catholics to have a wide circle of friends their own age as opposed to these times.