Breakdown of Estoy nostálgico; ¡quién tuviera el vigor de la juventud!
de
from / of
tener
to have
estar
to be (location/state)
la
the (feminine)
Questions & Answers about Estoy nostálgico; ¡quién tuviera el vigor de la juventud!
Why does ¡quién tuviera...! translate to "If only I had..." instead of something with "who"?
The structure ¡quién! followed by the imperfect subjunctive is a set phrase used to express a strong, personal wish that feels difficult or impossible to fulfill. Even though it literally looks like "Who might have...", it actually functions as "I wish I had..." or "If only I had..."
Since this means "If only I had," is the verb tuviera conjugated in the first person (yo)?
Grammatically, it is actually conjugated in the third-person singular to match the pronoun quién. In this sentence, the first-person and third-person forms of the imperfect subjunctive happen to look exactly the same (tuviera). However, if you used a reflexive verb, this third-person rule would become obvious: ¡quién se pudiera ir! ("If only I could leave!"), not me pudiera.
Could I use soy instead of estoy to say "I am nostalgic"?
You could, but it changes the meaning. By using estoy, the speaker is describing their current temporary mood ("I am feeling nostalgic right now"). If they said soy nostálgico, they would be describing a permanent personality trait ("I am a nostalgic person in general").
Why do we need the article la in la juventud when the English translation just says "youth"?