In the paper and pencil RPG world, if you want to generate a reasonable level 5 sorcerer player character or whatever, there are (usually) extensive systems to go direct to lvl 5 and skip the earlier levels. So just generate your NPCs / Monsters the same way. Obviously all paper and pencil RPGs have a "system" for generating level 1 PCs, and randomly simulating in a computer the lifespan of a character as it levels up doesn't sound all that hard or time consuming.
I fooled around with this idea in the 80s and it wasn't feasible computationally at the time, but it would work now. One funny problem I ran into is a stereotypical adventure eating monster tends to accumulate a lot of lower level adventurer cruft, not as much good stuff as you might hope for. Lets be realistic, a dragon is going to have to spend a large part of its lifespan eating unlucky dwarves if you hope to catch it with a cache of exotic gems harvested from those dwarves. A gang of thieves would on the surface have "harvested" lots of loot from peasants and occasional nobles over the years, but over the years most of that has drained out due to simple weight and need to eat. So thieves were another disappointment. As I recall corpse robber monsters tended to accumulate the best loot over time. Also nest type monsters, due to inability to move / spend anything they get, killer trees got the best loot. This can't be an original idea? I think this is how dwarf fortress generates people but I'm not sure?
For pathfinder, although I can't recall the name, there is an entire book (article? chapter?) just on custom NPC/Monster design techniques. Actually using a OGL licensed scheme might have issues. But the existence of one solution does imply the problem is solvable in at least one situation (LOL).
I fooled around with this idea in the 80s and it wasn't feasible computationally at the time, but it would work now. One funny problem I ran into is a stereotypical adventure eating monster tends to accumulate a lot of lower level adventurer cruft, not as much good stuff as you might hope for. Lets be realistic, a dragon is going to have to spend a large part of its lifespan eating unlucky dwarves if you hope to catch it with a cache of exotic gems harvested from those dwarves. A gang of thieves would on the surface have "harvested" lots of loot from peasants and occasional nobles over the years, but over the years most of that has drained out due to simple weight and need to eat. So thieves were another disappointment. As I recall corpse robber monsters tended to accumulate the best loot over time. Also nest type monsters, due to inability to move / spend anything they get, killer trees got the best loot. This can't be an original idea? I think this is how dwarf fortress generates people but I'm not sure?
For pathfinder, although I can't recall the name, there is an entire book (article? chapter?) just on custom NPC/Monster design techniques. Actually using a OGL licensed scheme might have issues. But the existence of one solution does imply the problem is solvable in at least one situation (LOL).