Yeah, that is a bit weird. Natasha is an adult during the assassination attempt, but then a few years later Antonia is Olga Kurylenko, who is older than Scarlett Johansson.

I mean Antonia’s face got burned off, I wouldn’t expect her to look like a kid

I don’t think Scarlett looks her age, I mean that as a compliment to her. She of course doesn’t look 18 either. They must not wanted to do a teenage version of her and just use Scarlett as she is. I didn’t notice any de-aging effects used. Anytime you deal with a film in the past, you run into a risk for errors with timelines and accuracy. I think this is one occasion they just didn’t want to bring in a teenage actor. Maybe that’s because it looks more personal to have Scarlett’s face there, as the one responsible for the bombing, then a younger actor portraying Natasha. That’s just my guess.

Yea the facial scars on Antonia hide her age too.

Actor ages don't really matter, like Chris Hemsworth, Thor is like 1,000 years old and Chris is 38.

^From all the examples you could have given, you chose the worst.

Couldn't think of any lol

Okay how about Vision is 3 years old and Paul Bettany is 50?

I mean, those are very very different cases...

Chris Hemsworth is playing a character that ages much slower than a human being. LOL

Oh ya...