G1 was the base of everything, and its a cartoon, they dont need to age at all! If they say something in the show it's proven. The creators wouldnt put in something thats not true. If they freaking say it straight out on the show it's canon, no matter what fans think
Sure Spike seems like he have the mental age of a 10 year old but he is still refered to as a baby. maybe not a newborn baby but a baby. So whether you like it or not, its a fact that cannot be changed by fans.