"Cuando sea viejo, pienso pasar un mes en África" - "Sea" viene del verbo SER pero en futuro. ;)

I unterstood, thanks :)

Cuando sea viejo, piensa pasar un mes en Africa =When he is old, he plans to spend a month in Africa pero esta situación es hipotética en el español y usamos el modo subjuntivo (But this situation is hypothetical in Spanish and we use the subjunctive mode) ;)

" Sea " is the " presente subjuntivo " form of the verb " ser " - to be. In this case it is used to refer to a hypothetical situation that may occur in the future. [emoji][emoji] Saludos Ciarán