How much does draft age matter for NBA prospects? A study (Part II)

This is a continuation of part I of a study on the importance of draft age in the NBA and the rookies arriving in the league. After we introduced the background and explored some historical context, it’s time to try and get the ultimate answer about whether or not prospects’ draft ages matter at all.

If you haven’t read the first part, I’d encourage you to do so, or at least to go through the introduction for a little explainer about the reasoning behind the methods and metrics used.

How Important Is Draft Age In Fantasy Basketball?

In order to get a better idea of how draft age affects a player’s overall career, I have analyzed all player seasons in the dataset (all NBA seasons from 1990 on) from that point of view. That means I have plotted players grouped by the age they were drafted at, and averaged their career fantasy points (FP; read Part I to better understand the metric if you need to!) per season. Again, I am not including only rookie seasons, but all seasons played by all players drafted in the dataset; that means that players are represented multiple times (ex. Vince Carter getting drafted in 1998 and retiring in 2020 means he appears in the dataset 22 times, from his 1999 debut to his 2020 retirement year; his data, though, always falls in the age-21 cohort as that is the age he was drafted at).

The answer this analysis can give us has to do, then, with how players perform in the NBA depending on their draft age, thus allowing us to know if those getting to the League earlier are primed to have more productive careers on a yearly-average basis. The chart below shows the average FP scored in a season, broken out by draft age.

The results can’t get much better. The only outlier in the chart is the Age-25 cohort but it only contains nine players which feature three (Dennis Rodman, Dikembe Mutombo, and Ervin Johnson) that totally skew that group’s levels of play in a very unique way. Other than that, everything else makes sense and allows for simple takeaways regarding draft age and career-wise performance in the NBA:

• We’re past the prep-to-pros era, but the three lone players to get to the NBA via draft while aged 17 were all fantastic: Kobe Bryant, Andrew Bynum, and Jermaine O’Neal all thrived and only injuries stopped Bynum from making it a trio of perennial stars in the League. Watch out for a potential abolition of the minimum age rule in the future, teens might be the next big thing.
• Players aged 18 also belong to past eras or just fall on the “older” side of 18 (ex. Kevin Durant being 18 years and 276 years old the day he was drafted).
• Moving on to the Age 19 cohort is where we enter the all-time era that comprises both players from the past that attended college for a season, and those belonging to the contemporary one-and-done era. And the group, on average, is the best one in terms of yearly average FP production with 1,500+ average FP per player-season compared to the second-best cohort (Age-20; 1,300+). There is a steady decrease in production from this age (one-and-done freshmen and international prospects declaring early) to all other age cohorts taking data-skewing outliers into consideration.
• Seniors, redshirt players, and other older draftees are, more often than not, busts that do not go on to have massively productive careers on a yearly basis. Most NBA teams seem to be aware of this, as there have only been 23 picks inside the top-10 of their respective classes that were drafted at Age 23 or older since 1980. Those include the likes of Michael Olowokandi, Sam Bowie, Derrick Coleman, and Rony Seikaly just to name a few. The only “viable” players to come out of those cohorts were Dikembe Mutombo, Sam Perkins, Mitch Richmond, Buddy Hield, and Andre Miller—a rather paltry hit rate.

In order to get rid of the Rodman Effect, which is to say outliers over/under-performing and skewing their cohort results wildly, I have looked at player seasons in which the individual FP tally that campaign topped 2,700 FP over the year. Although that might look too much like an arbitrary pick, the truth is that players to score that many (or around) fantasy points in a single season have historically been top-25 players (give or take) in that particular year.

You can forget about the red bars for a second. If you focus on the red bars—those representing the percentage of hit-seasons (1,700+ FP) from players of a certain age, you will see how there is a steady decline similar to that we already saw in the chart before this one. Working within the current era boundaries (that is, excluding players drafted at ages 17 and 18, which are voided from doing so these days), the Age-19 cohort is the only one in the dataset in which players have had more than 33% (up to 41%, in fact) of their seasons ending with at least 1,700 FP.

The distance between the freshmen/one-and-done group of draft entries and those declaring later (sophomores, juniors, seniors, and older) is staggering. There is an interesting similarity to be found between second-year and third-year college prospects declaring for the draft, as the Age-20 and Age-21 cohorts basically yielded the same percentage of hit seasons, only separated by one percentage point. The decrease is quite notable from that point to the senior (Age-22+) cohort of players, though, making it nearly impossible for such players to end having top-30 seasons at any point throughout their pro careers.

Solving The Mystery & What Is Coming

Judging by the results presented in this article after conducting our research, it is easy to see how younger players at the time of the draft are prone to end up scoring more fantasy points on a yearly basis during their pro careers. The results for those in the youngest possible cohort of ages (currently, 19-year-olds) are way above those from other older groups of drafted players, with the former hitting on more than 40% of their seasons compared to the others topping at just 33% in comparison.

The main reason, most probably, has to do with younger players that are actually drafted by NBA teams having better skill sets that allow them to compete against stronger competitors earlier in their careers. The youngest a player (or, for the matter, any professional in any working field) starts excelling and outperforming his competitors, the higher the chances are he steadily outperforms the expectations by playing to higher-than-average levels as he keeps developing.

Getting back to the present day and as introduced in Part I, all Evan Mobley, Scottie Barnes, Cade Cunningham, and Josh Giddey (with Franz Wagner and Jalen Green really close) would be considered in higher regard to their older peers (Davion Mitchell or Herbert Jones, to name a couple) even though some of those also performed to high levels as rookies. Over the long run, it is reasonable to expect the prior four (or six, if you count Wagner and Green too) to have the most fruitful careers.

Just for context ahead of next June’s draft, here’s a consensus top-50 Big Board split by draft ages of the players that are part of this year’s class. They are sorted vertically by their draft age in each year's cohort, and by consensus ranking in the event of an “age tie”.