The table below shows the top offensive winning percentages (OWP) for each 5-year age period. The plate appearance (PA) minimum was 2000. The "1 minus 2" column shows how far ahead of the next highest player the leader was. For example, Ted Williams, from ages 20-24, was .001 higher than Ty Cobb.
Now Ted Williams actually did not play at age 25 due to military service during WWII. Setting the PA limit at 2000 let some players like that in, guys who actually did not play all 5 years or only small parts of some other years. So the next table uses a 2750 PA limit.
Interesting that Bonds has the 2 highest 5-year periods but they are at very old ages, 34-38 & 35-39 (and he has the biggest edge over number 2). But one thing that makes his OWP's so high is that his OBPs were so high because he got walked so much. So those OWP's might not mean what they normally mean. So I also looked at the best 5-year hitting performances in slugging percentage (SLG) relative to the league average (RATE). Cobb's 160 from ages 20-24 means that his SLG was 60% higher than the league average. (.527/.328 = 1.60). )Here are the leaders.
Now the leaders with a 2750 PA minimum.
Bonds is no longer number 1. But the only guy to do better was Ruth from 24-28 & 25-29. The next highest RATE for someone besides Ruth or Bonds is Hornsby at 166 from ages 21-25. Then we have Ted Williams, whose best is from 27-31 at 164. Then Cobb from 22-26, also at 164.
The table below shows the top 30 seasons in relative SLG for players with 2750+ PAs. As you can see, except for Bonds and McGwire, high slugging is a young man's game.