How many squares of any size are in this grid?

Wallace died a wealthy, if somewhat odd, man without any living relatives. He left his money in four different cities for the first four people who could find it. The only clue he left was this poem:

Do not go solo,
Pairs up with a friend,
Though I hasten to add,
I’ll avenge my end.

What are the four cities?

Why can’t a man living in Okeechobee, Florida be buried west of the Mississippi River?

Marcus was 15 years old in 2010. In 2015 he was only 10 years old. How is this possible?