There should be a "HIN" (i.e. Hull Identification Number) on the transom in the upper right corner. It will probably start with either "DOR" (builder before ~2000) or "CDO" (builders after ~2000).
There are a few conventions, but from ~1985 on it goes like this:
1) First three letters indicate builder.
2) Next five are hull serial number which usually includes length but exact format varies.
3) Last four have to do with year, and will go "letter-number-number-number." The first of these is the month the build was started, with January being A and December being L. The second is the year it was started. The third and fourth are the model year of the boat. So, for example a HIN ending in J203 would mean a boat started in October of 2002 that is a 2003 model year.
If your boat is pre-1985 then we can go there.
Congrats!