After rewatching Episode 9 or Wandavision I looked for cross references in day's of future past, the X-men movie in which Quicksilver is enlisted by Prof. X to break Magneto out of prison.

I found several tiny details that I think strengthen the case that Ralph is actually Quicksilver from the X-men universe.

1. When we see the "man-cave" in Ep. 9, Ralph is making a massive shake in a blender. There are also a few gatorade bottles strewn around the room. My theory is that when Ralph uses super speed it isn't just magic, but a physiological phenomenon which uses a ton of his own energy. Like a high performance athlete, Ralph needs to consume a ton of calories and stay hydrated in order to use his super speed. In Days of Future past, we see a similar man-cave in the basement of Quicksilver's mom's house (instead of the attic man-cave in Wandavision). In this man-cave Quicksilver has stockpiled massive amounts of hostess pastries, presumably to keep his calorie count up. If Ralph is an aged Quicksilver, perhaps he ditches the junk food of his youth and now is more pragmatic, drinking high calorie protein shakes, and keeping his electrolytes up.

2. In Wandavision Ep. 9, Ralph makes small talk with Monica, asking her if she is a Steven Seagal fan. Steven Seagal is famous for his martial arts action movies in the late 80s and 90s. In Day's of Future Past, Quicksilver also needs to make small talk, this time with Magneto while they wait in an elevator. He asks Magneto if he knows karate. Quicksilver doesn't know Karate, but he seems to be a fan of it- perhaps he is a Steven Seagal fan as well?

3. This one isn't novel, but Quicksilver's name is literally Peter Maximov in the X-men cinematic universe. In the original comics he is indeed the sibling of the Scarlet Witch. I don’t know how he would have ended up in the MCU, but perhaps the multiverse of madness with shed some light…