Grimrock

Classic Age (pre-1985ish)
Examples: Wizard's Castle, nethack, the PnP RPGs
These are the historical underpinnings of the entire genre and represent the first attempts to port the rules and standards of the PnP to the new world of computers.

Golden Age (mid-80s to mid-90s)
Examples: Bard's Tale series, Wasteland, Dragon Wars, Might and Magic series, SSI Gold Box games, Sentinel Worlds
As the OP mentioned, these games allowed RPG fans a chance to play those games if/when circumstances didn't allow for getting enough people together to play. They typically featured the following:
•Player could create, and control, a party of characters
•Character had little to no control over NPCs added to the party
•Character creation was modeled on the dice-rolling methods of PnP
•While story and narrative were of great importance, it was as (or more important) to create a world in which the Player could help craft the story
•Combat was turn-based and tactical but limited by technology
•Actions had consequences and, in some cases, permanent death was a major issue (either due to game mechanics or save game systems)

Silver Age (mid-90s to early-2000s)
Examples: Baldur's Gate series, Icewind Dale, Fallout 1 & 2, Arcanum
As we enter the Silver Age we find technology improving so graphics, combat mechanisms, and breadth of the games all improve. These games follow, spiritually, from Golden Age games but start changing a bit -- partly because of new technology enhancements and partly as a streamlining of certain mechanics:
•Character creation starts focusing on point buy systems instead of rolling
•Player creates and controls one primary character who is the primary protagonist for the game story
•NPCs that join the party are fully controlled, in combat, by the player but provide personality and story in their own right (via dialogue or their own quests)
•Story is the primary point, propelling the protagonist along. Still well-crafted worlds but with the start of "chosen one" storytelling there is a little less wiggle room
•Combat becomes vastly improved by technological advancements; combat is still tactical based but only sometimes (truly) turn-based and starts heading toward real-time mechanics.
•Players are granted to ability to save anywhere and frequently to allow redoes of difficult obstacles or to reset after undesirable events

Modern Age (mid-2000s to present)
Examples: Fallout 3/NV, Mass Effect Series, Dragon Age series
The RPG starts to merge with the FPS genre, partly to accommodate console play and partly to become more immersive. Some previous traits carry over, and some new things change.
•Character creation starts focusing on point buy systems instead of rolling
•Player is responsible for the main protagonist and all story revolves around that character
•NPC companions may join the quest; dialogue, story, and quests from these NPCs are greatly expanded upon and they become essential parts of the narrative.
•Story is much narrower with the "Chosen One" issue front and center; even in open worlds with many character options the game dictates those options and becomes more of a branching tree than a truly open system.
•Combat switches to real-time with a heavy focus on first-person elements and mechanics. Tactics take a back seat.
•Players can -- and do -- save everywhere, all the time; this is partly to allow the ability to redo or backtrack, partly as protection from the increase in game-related bugs, and partly to see how things could go otherwise.