@some fag
 
What Vree said. We had a discussion on IRC and the term foalcon is for prepubescent characters, not ones below an arbitrary age limit.  
The reasons for this are that age of consent varies greatly between countries and even jurisdictions within countries.  
Additionally, in some countries like the US, the age for legal photo pornography is higher than that for consent, leading to more confusion on what underage is, and giving us the weird idea that you can hav sex with her, but she’s too young to take naked sexy photos of.
 
Additionally, if we accepted an arbitrary age limit, it would open the whole “who is what age?” can of worms. An example is that some may see some or all of the mane 6 as being below the age limit.  
That could lead to the ridiculousness of all mane 6 porn being foalcon, which would make the tag useless. BG ponies, OCs, and older versions of characters complicate matters further.  
Note that, even in this image, they could both be 19 and still be considered “teen” as the artist says.
 
This will be discussed more extensively by the mods I’m sure, but WingbeatPony, who is generally in charge of the foalcon tag and general tagging definitions, went so far as to outright remove the foalcon tag from this image.

Not me, but (implied) teen sex and foalcon are quite different things IMO

who keeps removing implied foalcon, did they even read the source?

Had to add foalcon. Source says Apple Bloom is just a teen.