Wikipedia provides an lengthy (for them) entry dealing with Gauguin here. Included is information that he began painting about 1873, but didn't do it full-time until starting around 1882-83.
Below are images of some paintings from his earliest artistic days to when his main style emerged.
A dark scene reminding me of Barbizon School art.
This is sketchier, the colors are brighter yet limited.
Here we find Impressionist-style brushwork and perhaps coloring (though this is an interior scene, not outdoor countryside).
Painted while they were still friends.
Here Gauguin is using somewhat stronger brushwork while maintining interest in color combinations.
This setting is a rarity for Gauguin.
A subject theme while he was in Brittany, though here his style is close-to, but not quite Gauguin.
Now he has been exposed to tropical colors -- an important factor of his later work.
Then, in 1888, Gauguin painted pictures in a wide variety of styles including the cloisonnist, strongly colored theme he became noted for.
Paintings from 1888
A nice portrait of artist Emile Bernard's sister.
An experiment using extremely bold colors.
Here he drops back briefly towards Impressionism.
This is perhaps Gauguin's earliest famous painting.