Here the meaning is correct. timeless="staying beautiful or fashionable as time passes", but I am not sure this translation is close enough. It does not use any verb for "stárnout". Consider just using the report when not asking a question although reports from discussions tend to be fixed more quickly.
I noticed that the app on the android doesn't always show the writing mistakes. For example I wrote "nestárneté" but when I go into discussion I see that correct is without accent on the last letter e - "nestárnete". When I practice on my desktop version it shows all writing mistakes.
In English grammar they are equally acceptable.
"František, you are not aging." and "You are not aging, František." are identical in meaning. English word order allows direct address vocatives, much like adverbs of frequency, to be flexibly placed in the sentence at either end. And sometimes (although often awkwardly in my opinion) even between the subject pronoun and the main verb (but after an auxiliary).
Technically even "You, František, are not aging." would be acceptable (although I don't particularly advocate it.)
There is simply no reason to move it. It requires huge effort to support the countless options it opens. No one says it is wrong grammar, but if there is any sequence of clauses, or just a word, separated by commas, follow that order. Just do that. It is the same like two words separated by and. John and Bob might be the same as Bob and John, but the order in the original will be required in the translation.
I understand, but this is literally the only vocative sentence I've run across that requires you to start the sentence with the name. As a native speaker and English teacher I find the vocative much more naturally placed (in English) at the end of the sentence.
And for example "Kateřino, kde jste?" accepts Where are you Kateřina? as a translation. Likewise " Matěji jste dobrý pritel." accepts "You are a good friend Matěj." as a translation. I just did a review lesson of the vocative skill and in all five sentences that began with the vocative I typed the name at the end of the sentence and it accepted all of them.
So I understand what you're saying, that not every niche translation of a sentence will be accepted, (Bob and John is a good example because you have a fixed order list), but this is the only sentence I've run across with the vocative that is requiring it to follow the exact Czech word order.
"František, you are not getting older" is among the accepted translations. But there is no report for this in the system, so we cannot tell you why your answer was not accepted. Please use the Report button when you feel your response was incorrectly rejected. That allows us to see exactly what you wrote.