Is Jaylen Brown still a 'prospect'? Plus, NBA pick-six All-Stars and the best player without a retired jersey

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How long can a young NBA player be considered a prospect?

Although that distinction could be a matter of semantics, it has a practical impact on how we evaluate players in their early-to-mid 20s for trades and free agency. In his discussion of the Boston Celtics potentially trading for Kevin Durant on the Lowe Post earlier this week, ESPN's Zach Lowe highlighted the possibility of Jaylen Brown (who turns 26 in October) continuing to take steps forward in his development.

One of the factors the Celtics must consider as they ponder a possible Durant trade is whether Brown is close to a finished product or can be expected to grow from a one-time All-Star into a player in the mix for All-NBA spots. Let's take a look at what history can reveal.

Throughout the NBA season, I answer your questions about the latest, most interesting topics in basketball. You can tweet me directly at @kpelton, tweet your questions using the hashtag #peltonmailbag or email them to peltonmailbag@gmail.com.

(I'm also answering mailbag questions on YouTube.)

In addition to the main question, this week's mailbag also tackles "pick-six" steals in the NBA and the best NBA players never to have their jerseys retired.

"What is the prospect cut off? At what point is a player likely what he is?"

-- Seth

This is an interesting question in part because of the different definitions currently in use. For symmetry, our annual top 25 under 25 rankings make age 25 the point when players cease being prospects, while the Dunc'd On Basketball NBA podcast sets the bar slightly lower at age 24.

Realistically, there's no one point where players are what they are. It's always possible for individual outliers -- such as Kyle Lowry -- to develop into All-Stars in their late 20s. However, there probably is an age at which these kinds of transformations become far more the exception than the expectation.