Very little since there is no published sn data.
Early to mid-80s
Your early J frame model 36 Smith and Wesson was made in the year 1955 with the serial number that you have provided.
Early to mid 80s
early to mid 80s
Call Smith and Wesson and they will tell you. You will be in the early 80's time frame.
According to Smith and Wesson this gun was made in 1969 and is an early N series.
Late 1975 - Early 1976
Your serial number indicates that your early model 36 was made in the year 1954.
Either late 1800s or early 1900s
Rohm and RG revolvers were made in the early 1960s, and banned from import to the US in 1968. They are of very low quality and worth, and there is no known database of serial number info.
The Smith & Wesson Model 37, known as the Airweight revolver, was produced starting in 1952. The serial number 21JXXX indicates it was manufactured in the late 1970s to early 1980s, as the "J" prefix was used during that time period. For an exact year, you would typically refer to Smith & Wesson's serial number lookup or production records.
Call Smith and Wesson and they will tell you. Yours is sometime in the early to mid-80's.