How small is the world?

Metaphorically speaking:
Let's say that during your vacation in France you enter a café and are about to order. As you stand in line waiting, the person in front of you turns around and appears to be your old class mate from elementary school.
Most probably, even if that person was only a friend of a friend, you'd start to talk. One of you will either think, or say, "oh, the world is so small!" and then you'd end up drinking coffee together.

That got me thinking, how small is the world really?
I was studying but got distracted by this thought and as I reflected I was looking out the window and saw a small bird sitting on one of the branches of the tree in the garden.
I said to myself: "the world must be so much bigger to that bird, than it is to me..."
Based on the thought that this might just be the case the size of the world must be proportionally smaller for a tall man, lets say 1,91 like myself, than for a child measuring only 1,30 above the ground.
Now, to think that in almost every "normal" case (I don't like the word normal), overlooking the fact that we shrink when we get older, it's true that with age comes height and vice versa.
Another parameter is that with age comes experience and I believe in most of the cases the source of imagination is greater in younger days.

The conclusion must be that the size of the world somehow must be inversely proportional to the size and age of the person.
Back to the initial reflection; the bigger and older we get, the probability of bumping into one of the unexpected meetings must then increase, yes?

I'm growing bigger and undoubtedly I'm also getting older, therefore my world is shrinking - and that means I need to buy more coffee.