Estar for past characteristics that should go with ser but can go with both actually?

I promise this is not your average "I didn't bother checking the wiki nor search at all" post.

So I stumbled upon a song and the lyrics are "Yo cuando estaba más joven/ De esas penas pasé tantas".

I read at some point that both ser and estar can work for age, using estar to better highlight the change or perceived change. But that ser is far more common.

Is that the case here? Is this just artistic liberty or actually correct? The fact that there is another song literally called "cuando era más joven" makes this even more confusing.

Many thanks!

submitted by /u/lorin_fortuna
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