So, the first thing to do is go the main forum here and look at the "Best of Forum" and search for contrarian23's work on fatigue.
The answer isn't simple because equally crucial are your pitch counts based roughly on the formula 15 pitches per inning, (for most pitchers, a little fewer for some deadball pitchers who threw few BBs and Ks), and the IP/G in real life of your starter.
A pitcher whose real life average innings per game (IP/G) was 6 cannot be used to pitch 8 innings or 7 most of the time. They will crash.
At the same time, a pitcher with 8 or even 9 IP per game if they have 260 IP overall (260 IP times 15 = 3900) cannot be used every third day (162 divided by 3 = 54, 3900 pitches divided by 54 = 72 = roughly 5 innings - a little less actually) for those 8 or 9 innings.
If they are in a four man rotation that same pitcher, if a first or second starter, and so expected to make 41 starts (3900 divided by 41 = 95) can throw 95 pitches a game, or around 6 innings on average, but can occasionally go up to the say 8 IP/G they did in real life - so you can set the lower number in that case to 95, the higher to 120 (15 times 8 innings = 120), but if you see his fatigue numbers showing he is being overused, cut that higher number back quickly.
Keep in mind that 260 innings in real life with an IP/G of 8 would be 32 starts in the season, so a five-man rotation on his real life team.
Pushing him into a four man rotation is doable, in a three-man, only if you have a spot starter AND are ready to set his pitch count very low in terms of IP per start for your team.