Daryl Morey (Houston's GM) uses a formula based on thousands upon thousands of data points. When he was first starting out, he had some strange results, but when he better accounted for age, he said the formula became much better and was a much better gauge of where a player might end up. Morey's conclusion, age matters a great deal.
That said, a lot of his strange results were looking at a 19 year old freshman vs. a 23 year old senior. I suspect there is a lot of difference between a 19 year old freshman and a 20 year old freshman.
EDIT: here is the article. very long but a very interesting read.
http://www.slate.com/articles/arts/books/2016/12/how_daryl_morey_used_behavioral_economics_to_revolutionize_the_art_of_nba.htmlHere is the part of the article about what I was referencing above
That year the Rockets had the 25th pick in the draft and used it to pick a big guy from the University of Memphis named Joey Dorsey. In his job interview, Dorsey had been funny and likable and charming—he’d said when he was done playing basketball he intended to explore a second career as a **** star. After he was drafted, Dorsey was sent to Santa Cruz to play in an exhibition game against other newly drafted players. Morey went to go see him. “The first game I watch he looks terrible,” said Morey. “And I’m like, ‘
Edited. Profanity and masked profanity are against forum rules and may result in discipline.!!!!’” Joey Dorsey was so bad that Daryl Morey could not believe he was watching the guy he’d drafted. Perhaps, Morey thought, he wasn’t taking the exhibition seriously. “I meet with him. We have a two-hour lunch.” Morey gave Dorsey a long talk about the importance of playing with intensity, and making a good impression, and so on. “I think he’s going to come out the next game with his hair on fire. And he comes out and sucks the next game, too.” Fairly quickly, Morey saw he had a bigger problem than Joey Dorsey. The problem was his model. “Joey Dorsey was a model superstar. The model said that he was like a can’t-miss. His signal was super, super high.”
That same year, the model had dismissed as unworthy of serious consideration a freshman center at Texas A&M named DeAndre Jordan. Never mind that every other team in the NBA, using more conventional scouting tools, passed him over at least once, or that Jordan wasn’t taken until 35th pick of the draft, by the Los Angeles Clippers. As quickly as Joey Dorsey established himself as a bust, DeAndre Jordan established himself as a dominant NBA center and the second-best player in the entire draft class after Russell Westbrook.
This sort of thing happened every year to some NBA team, and usually to all of them. Every year there were great players the scouts missed, and every year highly regarded players went bust. Morey didn’t think his model was perfect, but he also couldn’t believe that it could be so drastically wrong. Knowledge was prediction: If you couldn’t predict such a glaringly obvious thing as the failure of Joey Dorsey or the success of DeAndre Jordan, how much did you know? His entire life had been shaped by this single, tantalizing idea: He could use numbers to make better predictions. The plausibility of that idea was now in question. “I’d missed something,” said Morey. “What I missed were the limitations of the model.”
His first mistake, he decided, was to have paid insufficient attention to Joey Dorsey’s age. “He was insanely old,” says Morey. “He was twenty-four years old when we drafted him.” Dorsey’s college career was impressive because he was so much older than the people he played against. He’d been, in effect, beating up on little kids. Raising the weight the model placed on a player’s age flagged Dorsey as a weak NBA prospect; more tellingly, it improved the model’s judgments about nearly all of the players in the database. For that matter, Morey realized, there existed an entire class of college basketball player who played far better against weak opponents than against strong ones. Basketball bullies. The model could account for that, too, by assigning greater weight to games played against strong opponents than against weak ones. That also improved the model.
Morey could see—or thought he could see—how the model had been fooled by Joey Dorsey. Its blindness to the value of DeAndre Jordan was far more troubling. The kid had played a single year of college basketball, not very effectively. It turned out that he had been a sensational high school player, had hated his college coach, and didn’t even want to be in school. How could any model predict the future of a player who had intentionally failed? It was impossible to see Jordan’s future in his college stats, and, at the time, there were no useful high school basketball statistics. So long as it relied almost exclusively on performance statistics, the model would always miss DeAndre Jordan. The only way to see him, it seemed, was with the eyes of an old-fashioned basketball expert. As it happens, Jordan had grown up in Houston under the eyes of Rockets scouts, and one of those scouts had wanted to draft him on the strength of what appeared to him undeniable physical talent. One of his scouts had seen what his model had missed!