I used the word, "bigger" instead of "older" which I knew DL was expecting. I got shot down, of coutse. And I reported that my answer should hsve been accepted.
Here is what "mayor" means. Higher.
As an adjective it means, higher, largest, biggest, major, high, bigger, senior, main, elder, utmost, big, chief, adult.
As a noun it means, senior, elderly, elder, chief, capital, boss.
It has a abbreviation which is, Maj.
What I get out of all this is that mayor means, superior.
Since we were previously taught that "mas + adjective" is the equivalent to a comparative adjective in English, it seems logical that "mas viejo" would be the same as "older". But I don't know whether this is an exception. I hope someone from a Spanish-speaking country can enlighten us.