No. Ancient grandfather means very old grandfather, while great-grandfather means grandfather's father.

each "great" that is pre-pended adds 1 more generation exactly. If you are looking for a general term, I would use "ancestor" or "forebears". http://www.thefreedictionary.com/forebears. Ancient just means very old, but not related to the number of generations. You can say "my grandfather looks ancient", it would be considered a bit impolite to say it directly to him though lol.

If not, 'ancient grandfather'=great-great-grandfather?