Answering yes to [“Were you alive 20 years ago?”] means you have a relatively loose definition of what constitutes “you” and so you shouldn’t object to cryonics because you fear that the thing that would be revived wouldn’t be you.

Not necessarily. My definition of “me” may depend on the context. If someone asks me that question, I assume that by “you” they mean ‘a human with your DNA who has since grown into present-you’, regardless of how much or how little I identify with him.