Since I started playing, I've read about two years worth of forum questions, and everything I've read seems to say that a player's ratings pretty much stop improving after 4 years. Could someone please clarify something about the timing?

If I have a player whose player card says "Pro Years: 4," does this mean that he's done improving? Or will be improve a little more until this fourth year is done?

Thanks.

Nothing is exact.  I posted a player yesterday that improved his glove into his 9th year.   It's not uncommon to see a player gain a point or two in the learned skills into his 5th/6th season.   But, when a player completes his 4th year, the vast majority of his improvement is over.

So, when it says "pro years: 4", does that mean he has completed his 4th year? Or is the 4th year still in progress?

Completed 4. 

Thanks, Mike and Dedelman. That's what I kind of thought, but I was hoping my 4 year guys might have had another year of regular development. I'll just have to hope for the slight increases in skill ratings.

For the most part, you can look at previous season's development and project that out for future seasons.

For example: a player's rating in some category improves 8 points between S1 and S2, 6 points between S2 and S3, and 4 points between S3 and S4 (the current season).  You can figure that, all else being equal (playing time, coaching, no major injuries), he's probably good for another 2 points this season, maybe another point next season, and then he's pretty much topped out.

IMO, n00bs make the mistake of worrying too much about what a player will be and no at all about what he is.   Once he's completed his 3rd year, it doesn't matter what he might become.   He's either useful or he isn't.