I had a late foal last year, in August, and as she's only six months old, I still think of her as a foal, although she will be in yearling classes, she'll probably remain my ''foal'' until she's quite a few months older.
My early foals (March/April ones) tend to get called yearlings in their yearling year (ie after 1st Jan) but late born foals (June/July) I always seem to refer to as foals or weanlings till at least the Spring as they just dont look like yearlings yet.
For showing there needs to be an easy cut off date for calculating age, which is 1st Jan, but it doesnt make me want to breed early foals. If I have a late foal then it probably wont be shown as a yearling. There's no rush.
LOL That's about right; my oldest is always eventually "The Old Mare" and the youngest is always "The Foal". I'm on my third Old Mare and The Foal is going to be backed this year.