@Minus  
I see absolutely zero reason to believe his age is closer to Sweetie Belle than Rarity’s. If anything the age gap between him and the CMC is just as large, if not larger, than between him and the mane 6.
 
I also find it amusing that you claim there is no point in trying to pin down his age and then you try and pin down his age.

It’s canon that he can change age at will (or by others), so why are there so many comments trying to give him an exact age? We’ve seen him go from baby to adult to baby to teenager to adult to baby… Do none of you realise you’re giving yourself an impossible task by trying to give him a specific age? He is physically just above a baby dragon the majority of the time, that’s why they call him that. Though his actual age is far closer to Sweetie Belle’s than Rarity’s.

Twilight: “You do realize I’m required by Equestrian law to report this, right?”

I’ll bet this all started with an intimate hoof massage… Applejack must have never told Rarity just how wondrous those dexterous claws could be.

@Trickquestion
 
That’s because there were different writers for those episodes. Consistent characterization is never a guarantee in any story.

@EmeraldArcher  
Again, that depends if we should be using D&D rules.

@Fanloser  
It depends. In D&D, Metallics are generally more wise, intelligent and calculating than pretty much any humanoid species.

@Fanloser  
Too true. In “Dog and Pony Show” he’s reckless but noble, in “Dragon Quest” he’s introspective, contemplative and adventurous, in “Owl’s Well” he’s neurotic and insecure, and in “At Your Service” he’s an idiot.

@Burned_Brony  
Actually, the way he acts changes on an episode, by episode basis.

@Background Pony  
That still doesn’t make him a literal baby. A baby can’t walk around on its own or fend for itself, nor can it speak. If we’re gonna call Spike young, then the term child dragon would be more appropriate.

@candrew  
Which isn’t to say that he’s a full grown adult mind you, just that trying to apply human developmental ages to a dragon doesn’t make much sense.

@Background Pony  
And yet that’s apparently enough for a dragon to grow to full size under the right conditions, and as such, makes him definitively not a baby by dragon standards either.

@candrew
 
I’m not saying that he can be considered a baby by pony standards, but on the other hand, if he just reached puberty, that means he’s 11-13 years old, 14 at most.
 
(Getting the hell outta here before this really goes out of hand)

GOOD SHIT SPIKE GOOD SHIT.

@Background Pony  
Well, considering we had an episode where he hit puberty and then decided he didn’t want any of that, it’s rather hard to make a believable case that he’s an actual baby.

@Burned_Brony
 
So him being ridiculously shorter than the rest of the dragons didn’t tip you off?

@SpikeSpiegel  
COS NOW YOU’RE A MAN  
A MANLY MAN MAN!

I don’t care if it’s technically fillyphilia, I absolutly LOVE the idea

Shouldn’t this be tagged “implied foalcon” or the draconic equivalent?

Apparently he was old enough.

Drink’s on me, boys! Last night our baby boy became a MAN.

Dayum.

@Fanloser  
Baby by what standards? Actual age? It would be fair to assume Spike is either a child or preteen in age, so he clearly isn’t a baby in age. Maturity? He has a job with responsibilities and can stay at home by himself, and is certainly wiser than a toddler could hope to be.
 
The individuals that have called Spike a baby are his pony friends and the other dragons. His pony friends aren’t exactly experts on dragon biology, and the other dragons were clearly trying to insult Spike because of how short he was compared to them.
 
He’s obviously not a literal baby, I don’t think anyone here can get away with saying that.

@Burned_Brony  
He’s also still referred to as a Baby Dragon.