Can you more experienced conchologists/malacologists out there
     help me with a few questions concerning the age of shells.
 
     1) I was wondering how long it takes most cones and cowries to
     reach their adult size?  That is when the shell is considered
     adult and no longer juvenile.
 
     2) Can you determine the age of a shell?  I know with some
     bivalves, you can count the number of growth lines to determine
     its age.  How do you tell the age of gastropods such as cones or
     cowries?
 
     3) Are giant sized shells very old shells or are they ones which
     just grew bigger?
 
     Thanks in advance for any and all responses.
 
     Ted Hu
     Montebello, California USA