The best way determine the year your house was built is to contact the Pinellas County Tax Records or Appraisers Office. I attached the link below. There are many features available at this site too; http://www.pinellascounty.org/public_records.htm
Another way to determine the approximate year built, assuming that the toilets are original, is to look under the tank lid - usually the manufatured date of the tank is stamped on the bottom.
We live in towns with the same name...Crystal Beach but I am in Florida.
Florida's Crystal Beach is a small Gulf side community with many older Florida style homes. Unfortunately, the community also attracts folks who come in and build mega mansions which tends to take away the ambiance.
Enjoy your new home!