Firered is basically the same as Red. HGSS is a direct remake of Gold/Silver, which takes place after Red. By the manga (and US release dates), it's 3 years. Emerald is an improved version of Ruby, which, by previous logic, takes place 2 years after Gold.
But what about Celio? International trading was created in Firered, when a Ruby and Sapphire were used to connect National PokéDexes. That's how you can trade with FR off the bat. I may have missed something, though.
Edit- Longest post I ever made with a Wii Remote.
Okay, Red is still alive during the events of Ruby- that's how he trades.