The adult Smurf stage is one that starts from the age of 100 to whenever a Smurf passes away.
Early adult years[]
In the early adult years (which would be from 100 to 400), a Smurf looks to be a productive member of Smurf society and is usually (if not always) given a particular vocation, though some adult Smurfs have entered a vocation from their Smurfling years. Also in the early adult years, a Smurf looks toward a member of the opposite sex to settle down with and start a family (in fanfictions where Smurfs are portrayed as a natively two-gendered race instead of a single-gendered race). In the EMPATH: The Luckiest Smurf story series, male Smurfs may experience the "Smurfette dream" which is their initial indicator that they are physically prepared to become Papa Smurfs.
Middle adult years[]
The middle adult years of a Smurf, or "middle age", would be from 400 to 700. It is usually around this age (in mainstream Smurfs media) that a male Smurf begins to grow his first beard.
Late adult years[]
The late adult years of a Smurf would begin from 700 and continue until that Smurf passes away.