Another issue to think about is what kind of time scales are we working with, and what kind of game play are you really looking for? And how are colonists represented within the game. Ideal game play growth patterns are vastly different if your colony plays more like The Sims vs an older version of SimCity. One having each colonist as a distinct entity that must be tracked, vs a fairly simply integer comparison of NeededWorkForce isLessThan TotalPopulation isLessThan Housing and LifeSupport.
If the game is "in for the long haul" and each colonist is a distinct entity then it could be that you have a preset 'seed' population that arrives in cold storage. You have X number of colonists on life support, and then have set needs you have to achieve before you are allowed to unlock the next batch. ie: Enough food, air, and water production to keep everyone alive, plus some minimum level of living space. After you exhaust your initial pool you then are reliant on new colonists that the colony itself can produce.
By that point in your game play you can be getting into building more automated systems to replace your initial constructions, rather than say needing 12 workers to control your main fabrication facility that produces parts for buildings, you can instead crew it with just 8, freeing up 4 people to work else where in your expanding base.
This lets the player 'keep going', and expanding their colony, but doesn't drive up the processing requirements as much if you are simulating each colonist beyond being just a number. "New" colonists then trickle in far slower as youth develop and are trained, but can be offset by older generations beginning to die off from age or accidents. It can also open the door to interesting plot points and choices, especially if the game relies heavily on colonists personality and factions.
Maybe you could have the option of deploying Clones. Clones can be matured faster than natural birth children, meaning they are ready for the work force sooner, but may be opposed by members of some factions. Similar with 'simple' advanced robotics that merely reduce labour requirements in facilities and 'complex' advanced robotics that can be full blown AI crew members. Maybe some colonists don't mind that their food was totally grown by mindless machines slaving away in a aquaponics bay somewhere at the edge of the colony, but when a dozen androids march by to their next job site things will feel a little different. (Especially if you have some kind of revolt and oppression mechanic.)