This is the 2368th most frequent Spanish word.
viejo
Old.
Here, 'viejo' is an adjective describing the advanced age of the speaker's grandfather.
Mi abuelo es muy viejo.
My grandfather is very old.
In this sentence, 'viejo' means long-time, referring to the extended duration of the friendship.
Hace mucho que no veo a mi viejo amigo Juan.
I haven't seen my old friend Juan in a long time.
Here, 'viejo' is used to describe the car, suggesting it's been around for a long time or is worn out.