Creo can make an adult out of a child because it is an improvement. Perdo aging spells will have no effect on that same child for that very same reason, but will work on an adult (q.v. Bane of the Decrepit Body).
I cannot see why that reasoning shouldn't be extended to plants and animals. Now, as to whether Creo aging will effectively reduce the lifespan of its target ... a SG could rule either way. It is conceivable that aging rolls would be based on the target's true age ... or that could be a "major side benefit" from experimentation by someone hoping to break the limit of aging.
I would probably allow it, but not in 10 seconds. This would just help you grow fine plants in the normal amount of time, not speed up growth in any way.
The same goes for your humors thing. This could maybe give a bonus to resist illness and such, but could not perform instant healing.
Creo Herbam guidelines deal specifically with bringing plants to maturity in strangely short time. Level 15: "Bring a plant to maturity in a single day or night. The accelerated growth only happens during the duration of the spell, so full maturity requires a Sun duration spell cast soon after sunrise or sunset."
... seems to be implicit in this that the effects are natural and permanent, only speeded up. So if the tree happened to bear fruit, I'd say the fruit would be nourishing. It's not summoned from whole cloth and gone in a moment, after all.
And indeed, there is a level 15 ReHe guideline too. "Make a tree blossom out of season, in a moment."
Yes, that's the way I read the guidelines too.. .. because a spell that takes all sun duration to grow a plant.. then goes back to normal at the end is rather useless
The very fact it takes so long to work in most cases is because it's being encouraged to grow faster not instantly (which is a natural thing and so doesn't go back.. that's how magic works when it doesn't break the laws
I think it is fine to make food this way. And to have it nourish. Even has a nice feeling to it.
And if it beomes a game-breaker in terms of the economic integrety of the setting (as was one of my arguments against the non-ritual food) you could always find ways to limit overuse.
Allow this, and you also allow a CrAn to mature cattle... It will become a rather common way to make/save money, and will take some focus away from the economic difficulites for a covenant...
Not saying that this is bad, just that you should be aware that what applies to one sort of maturation spell applies to all... (An, Co, He)
I just think of these things and if my SG doesn't like it, he will send a plague of locusts or frost or apple eating marauders.
I wasn't even thinking of the covenant, actually, I just have a character that eats alot... but Cr An should work on the cattle, I would think. Huh. Good idea.
As for side-effects? Warping I'd say, ingesting magically altered food might have to be the next big thing for grogs to protest against as their offspring gets marty-felman eyes, webbed hands and develop a longing of Ry'leth...
True - and no quarrel there. But as I mentioned you could think of ways to limit it - and Fruny and Oberoten already mentioned some great and easy ways to do that.
And making the crop or chatle infertile more or less puts a cap on letting it undermine setting economy, as the seed for next years fields are as important (if not more important) as the grain used for consumption. But using Creo magic to mature something still has great benefits (a sudden boost in production if in need and a certainty that the target reaches maturity without being cut short by vermin, disease or other hazards).
Warping adds colour, and can be made severe enough to possibly limit overuse. Warping might be more than on just the nature of the matured (behaviour of lifestock or taste or effects of eating the meat, eggs, milk or grain), it could also be used as an effect on the surroundings aka "enviroment". If whole fields of crops are matured as a regular practice, you might think of ideas (and nice storries) about local water sources drying out, possible annoyed faries, or even a metaphysical 'deadening' of the power of creation (local children growing slower, women becoming less fertile, wounds recovering a bit slower, the orchad stagnating and the herb garden slow to replendish itself).
That would be a really good pomegranate... or a funny water baloon.
