You are being generous with the cut off here. LOL. I think it is somewhere around 25-30. I have seen so many posts on reddit forums people saying they are struggling to make friends between ages of 25-30. And most of the times the answer is that social circles kind of stop developing after university years. And this is not limited to GTA / Canada. Similar posts can be seen even in other major cities NYC, Chicago, Sydney etc.After a certain age, you do not really become close to new folks. I guess 40 or so is the cut off or may be earlier.
I think one thing which may have impacted this is probably dating apps. Before dating apps people did expect to go out in bars or other social settings to meet new people. With apps people don't want to make that effort and these apps are skewed towards the desired top 10% or 5% of the profiles and rest of the folks.