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Effects of not growing up?

Let's say I have a bunch of pre-pubescent children (circa 8-12 years old). Let's also say I subjected them to some drug/process/whatever that caused them to stop growing. In particular:

- Whatever height they are when exposed to the process, that is how tall they will be. Same with proportions.
- Visible effects of aging are retarded, at least for a while. Several decades later (assuming they've "kept in shape" in such a way that their fat/muscle mass hasn't changed significantly, and excluding deliberate cosmetic alterations), their appearance is remarkably similar to when they underwent the process.
- The process involves physical/genetic changes, but isn't itself ongoing. (IOW, it might create organs or alter stuff, but doesn't involve a permanent nanite colony or ongoing magic, nor does the process need to be repeated/refreshed periodically.)

Is it plausible that these are the *only* effects? Or is the appearance of not aging unrealistic/unbelievable unless it also brings along biological immortality and/or some sort of super healing factor? (If they *can* still die "of old age", does the appearance of age ever "catch up" to these "children"?)