What might have (previously) been: Socks Seybold and retrograde projection

Can you project a baseball player's performance into the past?

I have an unusual interest in Socks Seybold, who played for the Philadelphia A's in the first decade of the 20th century. He was my great-great-great (I think) uncle--by marriage, so he deserves no blame for my own limitations as a player.

My man Socks was an excellent hitter. After a brief stint with the Reds in 1899, he began playing full-time for the A's in 1901. According to Jack Kavanagh, Connie Mack brought Seybold with him to Philadelphia when the American League commenced operations. In his second full season, Seybold set an American League record for home runs with sixteen, a record that would be broken by Babe Ruth 17 years later.

Seybold hit very well from 1901 to 1907, all of his seven full seasons: he was in the league's top ten every year in slugging percentage, and in the first six of those seasons, he was also in the top ten in OPS and OPS+. His career OPS+ mark (probably as good a quick indicator of hitting quality as any) of 130--that is, 30% better than league average--ties him with Roberto Clemente and Wade Boggs, and puts him ahead of the likes of Dave Winfield, Carl Yastrzemski, Eddie Murray, and Jim Rice. Obviously, his was a short career--only seven full seasons--and Kavanagh writes that "an injury in 1908 ended his major league career."

Simple enough, right? A good career shortened by injury. So it goes.

But here's the key fact: when he incurred that injury in 1908, Seybold was the seventh-oldest player in the league! He was already 37 and almost certainly at the end of his playing days. Born in November of 1870, Seybold was on the old side of 30 when he began playing full-time, already in the typical declining years for a baseball player. I don't know why didn't begin playing earlier: in those days, I imagine he might simply have gone unnoticed as a local star for years, or wanted to stay in a safer or more respectable trade until a solid professional opportunity came along.

We have lots of tools, such as similarity scores and Bill James's favorite toy, to look at a career cut short and project a hypothetical future. As far as I know, we have none that help us see what the missing first half of a career might have looked like. I can say that eyeballing the thirtysomething years of the Hall of Famers I mentioned above, only Clemente (definitely) and Winfield (possibly) look like they might have posted an OPS+ of 130 or better at the ages Seybold played.

I wonder whether a retroprojection tool might be useful not only for cases similar to Seybold's but also for examining more recent players who might have been brought up from the minor leagues too late.