Re: Where are the oldest aikido dojos in the world?
I don't know if these count, as they moved early in their existence, but the organisations are still training. I guess they don't seem so old compared to Hombu and Iwama.
1954 - Sunadomari Sensei's original Manseikan dojo in Kumamoto.
Unfortunately it appears to have been torn down (Google Street View showed it still standing in 2015, but not later). That was opened in 1954.
1968 - Australian National University Aikido Club, Australia, founded by the first student of Sugano Sensei. Moved once to the new sports centre dojo (constructed by knocking out the dividing wall between two squash courts). The dojo was rebuilt during major building renovations about 20 years ago into a proper facility.
1970 - Fukuoka Dojo, Japan. Though due to the dojo moving once, Takasago dojo here is actually older. The current Fukuoka dojo is in a 100 year old building.