Can i find the year of of manufacture of my old johnson 25 hp outboard motor by its serial number?

Ed,
Near as I can tell, it's a 1979. As of 1980, Johnson/Evinrude used two LETTERS at the end of the model number to designate the year. (See attached) Your model number ends in a number and letter (1A) which leads me to believe it's earlier than 1980. Prior to 1980, the last two numbers of the serial number were the year. That's how I surmised yours is a 1979, by the last two of the serial. G02651879

Hope this helps.
Fred-
Outboard Engine Serial Number Year Match up

not generic look down under motor by swivel bracket or lift cover off
Reference com What Your Question Johnson Outboard Motor model numbers and code

the serial number is not consistent with johnson serial numbers as all have 2 letters followed at the end by 2 numbers which indicates the year of manufacturer 9 ( ft17598 indicates it was mahe in 98)
There are pages on the net explaining when a serial number is used but it must be old as johnsons have used model numbers for identification since 1960's
probably better if you take it to a johnson service dealer as they may have the johnson factor list for serial numbers as you will have to identify it to get parts
go google and type in manufacture date of 40s johnson td 20 outboard serial number 63191
if that shows no results just cahange some words in the search

To get the year of Johnson and Evinrude outboards use the word "INTRODUCES". Each letter corresponds to "1234567890" respectfully. It's best to check with a model year reference book, but this motor's model number contains "CC" which would indicate it's a '88.

1978 It is in the model on an Evinrude. 6804.... 6 HP.....1978