viejo vs. anciano vs. antiguo

Hola Gerald

The adjective "viejo" applied to people generally sounds negative if you are talking about someone that you know and saying it directly to them. In a more neutral way you could say for example: "Hoy he visto a un hombre muy viejo en la calle". (in this case, as it's not directly said to the person, it's OK)

To avoid the negative connotation, we'd use "mayor" instead, which sounds more polite: 

Un amigo mío, que es ya mayor, me va a visitar hoy.

A friend of mine, who is old, is going to visit me today.

However, we use "un viejo amigo" with viejo placed in front of amigo for the phrase: "an old friend", i.e you've been friends for years. So:

Un viejo amigo (mío) me va a visitar hoy.

A friend that I've known for year is visiting me today.

The adjective "anciano" is for "really old people" (I'd say 90 yr old plus), so:

He visto a un hombre anciano en la calle.

I've seen a very old man on the street.

The adjective "antiguo" is not used for people, only for things that are old:

Tengo un reloj muy antiguo en mi salón.

I have an old clock in my living room.

Ayer vimos una película antigua, de los años 40.

Yesterday we watched an old movie, from the 40s.

I hope this clarifes the uses of these different adjectives. They are indeed confusing sometimes.

Saludos

Inma