I've been seeing this question come up time and again over the past several years, and it's understandable when you consider that often, the people asking it come from the deprecated, legacy silo space.
"When I follow someone, why don't I see their older posts?" - or some variant of that.
For example, when you follow someone on Faceplant, you see everything going back historically; because it's a silo. One theoretical host (server) with a centralized database that everyone using that host/service has in common.
When you follow someone in the #Fediverse, you begin to see their posts in your timeline/feed moving forward from the point in time that you follow them, because we're talking about the database local to the Fediverse server instance where your account is.
Okay kiddies, let's be real careful with this - again, Be really mindful, and especially careful here. You can accidentally DoS your box very easily if you're not, but here's a useful tool for those occasions where you want a history you might not normally have:
