I’ve only drawn Astra as a kiddo, so here’s her as an adult! This is what she’d look like throughout Cassiverse. The main difference is that she grows tufts on her “elbows”, where her stomach is. This is a super rare trait! It’s commonly observed in earth ponies, not so much in pegasi. Pegasi are occasionally born with a similar feature, except the “tufts” would be feathers.
 
The only other noticeable change is her wingspan. Rainbow Dash was worried for a while. Like her adopted sister Scootaloo, Astra’s wings didn’t seem to be growing past the down-feather stage. For years, Astra simply just couldn’t fly. Usually pegasus foals are able to fly by the time they’re 4 or 5, sometimes earlier. Astra’s wings stayed pretty small till she reached 15, when she hits a sudden growth spurt. After many, many more growth spurts, she outgrows her entire family and has the largest wingspan of all of them, beating Dash herself.
 
She’s the youngest sibling and naturally the most spoiled. She ends up outgrowing both her siblings by quite a few inches.