From what I have noticed, age does seem to have an effect, but it seems to be more of a minor one; the more children they have seems to have an effect (could just be randomness too); time of day seems to have an effect -later in their day they are more likely to be tired. Health seems to have an effect - but I have seen extremely weak peeps have full energy after a good nights rest, they just move slower. Healthier peeps seem to have more energy over the course of the day (use of treadmill upgrade, feeding the fruit from the varied section of the store).

How many "upgrades" I have purcased seems to have an effect (the more 'recreational' upgrades seem to give them more areas to regain energy by rest/playtime - i.e. hammock, swimming pool, pinball).

Thanks Magesteff for your post hints, I have been focusing on upgrading my carrier rooms and have gotten very little house upgrades. I look forward to discover the effect they have on energy!

i dont believe shutting the game down or the computer off has anything to do with the energy levels, this game just like VV, runs even when not being played, just depends how many naps they take, if they stay full, how hard they work, etc

UnSaintly-- I have actually noticed full energy resotred if I leave them alone at night -- I put them all to bed, then shut the computer and check back on them the next day. They are fully rested. It does run on real time like VV but unlike VV where energy wasn't an issue, they do restore with sleep. But the key is to not open the game up again after they're tucked in ; ).

i never pause my game! i do close it but i never pause it! i dont see alot of issues with energy til night time. (their nighttime)