Mamono become sexually mature before the age of 10.
Mamono don't go after young boys until sex becomes safe both physically and mentally for them(exact age is unknown)
Overall this is a good question, if your choice is either to marry your daughter or have her mark a young boy before they are grown up. How can mamono be single while adults?
@The Vaudevillain Veteran You're missing the point of the question.
Basically your answer says that mamono don't grow up single but either marry their dad or a young boy early on.