Or, there are animation/layout errors in this show.

@Vree
 
@ChargedUpIsAwesome  
Yeah a fully. You guys said it like the main 6 are not old enough to have kids.  
Or aren’t they?
 
 
@Nyperold  
Yeah screw it lets go with that.

Lyra, Minuette, Bon Bon, and Derpy were all fillies at that party. A Post-Rainboom Event. Yet, all were grown mares at the Summer Sun Celebration that inspired Twilight Sparkle to pursue magic. A Pre-rainboom Event.
 
I have to assume time travel is involved.

She has a daughter

She is a host to a Goa’uld symbiote who is too inebriated at any given time to become a capable System Lord. It is also perpetually repairing the damage Berry does to her liver.

What’s wrong with Berry Punch being older?
 
She has a daughter (Ruby) in case you forgot.

Bacground ponies have no real ages, since they’re just extras, no real characters.

@Background Pony #3B41

The correct answer is old enough to be a milf. Shame on all of you

https://derpiboo.ru/555939  
She will see the end of Equestria

@PonyLover99  
@HJSDGCE  

@PonyLover99  
Oh hell…

She’s Cheerilee’s mom.

Highlander.

She’ll never tell….

@Background Pony #BF33  
Well, that’s just it. You can’t really argue Canon against Non-canon correctly.

@Background Pony #BF33  
Comics is comics  
Show is show  
Having two different headcanons is the only way to preserve your sanity.

@Background Pony #BF33  
The show (maybe that’s just the animation team’s doing) doesn’t really seem to be bothered with keeping track of comic canon much of the time. See also Fleetfoot in Rainbow Falls.

So, if all the mane 6 got their marks after seeing the rainboom then…
 
I’m curious, if Pinkie had this party with filly Cheerilee, then she would have already gotten her cutie mark from seeing the rainboom. As her first party was with her family on the rock farm.
 
However, in both Cadance/Shining Armor and Sunset Shimmer comics Twilight is cutie markless. Yet we have a fully grown set of ponies in each comic, Cheerilee, Cogate/Minutte, Twinkieshine, Lyra, and so on.
 
So how can they go from fillies (cutie mark Pinkie) to near grown mares (no mark Twilight) if the mane 6 got their marks on the same day?
 
As far as I’m concerned stick with your headcanon ages or we’ll be at this for days.

So she might be… <gasp> 30? 40?

She is immortal, she has inside her blood alcohol content of princesses.

Berry Punch has so much alcohol in her blood it acts as embalming fluid. She is effectively ageless.

@Background Pony #234D  
You got it backwards, FLUTTERSHY said she was a year older than PINKIE PIE.

@Background Pony #A84D  
wibbly wobbly timey wimey

Just how old is Derpy Hooves? She appeared fully-grown in “The Cutie Mark Chronicles” in Twilight Sparkle’s flashback.