There are many soccer leagues in the US. Anybody can play soccer
no matter where they are or how old they are. There are club teams
for children and adult leagues for adults. You just have to search
around and find out what leagues are in you area.
There are too many to count. There are dozens and dozens of
basketball leagues, a few American football leagues, soccer
leagues, many baseball leagues, and so on. There is no kept count
of professional athletes.
Many MLB organizations have systems down in the Dominican
Republic, Mexico, etc. they are similar to the minor leagues in the
US. scouts draft players and if they develop enough skill, they
come to America and play for the US. teams.