Serial No. Clue to Age?
 

The FS 12 Sovereign bike I am restoring has the following serial nos.
718 472 851
8L 9L 0063
Could the age of the bike be determined by these?

It's an entry level bike obviously although it does have lugged tubing and shimano derailer. The freewheel says cyclo 72 Made in France and the rear wheel says:
RIGIDA
27 X 1 /14 Made in France Chromage Superchromix

Serial numbers are useful if you know the code. If you don't, they're not.

The Shimano derailleur probably has a date code on it, though.

You can get a pretty accurate idea by dating the components even if you don't know the system that the frame maker used.

See here: http://www.vintage-trek.com/component_dates.htm