Q: I hope I never get to be a forgetful old prune like you! とはどういう意味ですか?
A: A prune is a preserved plum that often looks wrinkly. However, informally, when you call a person a “prune,” it means a disagreeable or unpleasant person.

However, in your phrase, it doesn’t sound very rude. It sounds like a joke.
Q: forgetful
A: Forgetful is an adjective used to describe people who forget or don't remember things. "The man was forgetful. He didn't remember his lunch."


Q: How do you say I'm forgetful in Korean? は 英語 (アメリカ) で何と言いますか?
A: wrong language
Q: what does forgetful mean ? は 英語 (アメリカ) で何と言いますか?
A: @juanjix63: It is a quality someone can have, meaning the forget things often.


Q: How come I'm so forgetful. (なんでこんなに忘れっぽいんだろう) この表現は自然ですか?
A: Yes, you can say that too.
Q: She got forgetful rapidly. この表現は自然ですか?
A: that does not sound natural. if you are talking about someone being constantly forgetful, you can say: “She forgets quickly.”

however, if you are saying it in terms of illnesses, then it’s called ‘dementia’. but i dont think this is the context you are using it in.
Q: 1. What was I talking about? Oh, I'm so forgetful!
2. What was I thinking about? Sometimes I'm kind of forgetful.
3. Could you recommend the best way to improve my English skills?
4. Could you suggest the best way to learn English?
☞ I made random sentences. Are they natural or not?
A: Yes, they all sound natural. No. 3 could be made better by using the word "suggest" instead of recommend: "Could you suggest a way to improve my English skills?"

I've read several of your questions and your English is excellent. Have you read The Joy of English by Jesse Karjalainen? I think you would enjoy it.
Q: I'm so forgetful この表現は自然ですか?
A: That's definitely natural! :)
Q: When we age, we may become forgetful and a lot of problems appear. Not to mention some wrinkles may give away your real age. Because of that, a lot of people try to have plastic surgery to look younger, but I don't think it's a problem. この表現は自然ですか?
A: Overly very well put, however a couple of things managed to snag my attention.

1. Consistency of pronouns; since you started the article with 'we', it sounds off when the next paragraph switches abruptly to 'you'.

2. 'Try HAVING (a) plastic surgery (performed/done) (in order) to..', though I'd personally say 'a lot of people opt for/reach out for/go for/seek out plastic surgery..'