that doesn't make any sence if Sunset was a child of Starlight and Sunburst then why does Sunset have the same age as Twilight

I have a theory that Sunset and Sunburst might be brothers and sister for example the alternate universe shining armour and Twilight

Shinging Armour=Sunsburst

Twilight=Sunset

as you can see if we put charatchers in alternate universe Sunset and Sunburst are brothers and sisters and for Twilight and Shining armour we see that they can be related but if we swap them back to their normal selfs you can see Twilight and Shining Armour as brothers and sisters

In Twilight family we can see that her brother and her parents are having the same star cutie mark

for Sunset and Sunburst and his parents we can see that they all have the same sun cutie mark

so that could be meaning that Sunset and Sunburst are brothers and sisters (if you like this theory then comment or reply to me if you think that Sunset and Sunburst could be siblings if you don't like this theory then get the hell out of my comment)