Fully half of the expats living here do not apply for residency which you can get as a pensioner or a rentista. Most people simply go to another country every 90 days (180 with extension). You do not have to leave for three days, just cross the border so your passport is stamped.
Obviously, most expats are retired but there are more young people showing up. San Juan del Sur tends to be a younger crowd.
More information at my website nicaragua-guide.com.
Regards
Darrell