Let me maybe help clear this up: TFwiki has pages for both canon and continuity.
I did an assignment on this back in uni, besides being about clearing the way for/selling new toys TFTM is a pretty clear example of classical Hollywood cinema model and the 'heroes journey' monomyth - which often involves a young, brashAll-American malehero type overcoming obstacles and acquiring wisdom, usually by outgrowing/discarding old views and opinions as a consequence of his trials/journey. It was a while ago when I wrote it, but to give the three examples that IMO best illustrate his 'path to matoority', we have...
* "If you're gonna ride Danno, ride in style!" on Earth contrasted with Kup: "That's a ship?", Hot Rod: "Who cares, as long as it flies?" (learns to value substance over style),
* the dismissal of then successful use of the Universal Greeting (Allicons VS Junkions) (i.e. move from 'fight response' to 'diplomacy'), and
* "Don't we have anything better to do than tell old war stories?" VS "Doesn't this remind you of anything Kup?" (Hot Rod learns the value of experience/listening to your elders).
Then you get Kup's re-evaluation of 'Turbo-revvin' young punk' to 'I knew you had potential lad', and the way Hot Rod automatically takes over leadership from the de-Matrixed Ultra Magnus on the planet Junkionand selfishly involves an entire innocent race in a nigh-hopeless fight against a dark God to save his own world in the process. Of course, it is a kid's cartoon whose main point was to sell toys and so this isn't as overt as many other 'hero's journey' narratives (or rather gets lost amongst the sheer awesomeness of Unicron), but the progression is there once you look for it, and forms pretty much the main story to boot.
Basically, I submit that the 'physical maturity' (including lined face and vocals) is actually the least important aspect of Roddy's 'evolution' in TFTM, put in tosell toysvisually signify the (admittedly shallow) character development he'd already undergone. The S3 cartoon, in contrast, downplays/dismisses this for narrative purpose, most notably in Burden Hardest to Bear with the 'burden of command' schtick, but even then just repeats the process with that trite 'giri' moralising. The same thing sort of happens in The Ultimate Weapon, 'cos the brain is the ultimate weapon doncha know.
But then, the S3 cartoon makes Grimlock comic relief, and Galvatron an omnicidal nutcase, and has Unicron created by a puny monkey, so yeah...