He said that the average time for making Black Belt is about a year and a half
This I find very interesting, To be honest the time is really really short, and it make me very skeptical if all you want to do is learn some techniques and have a work out then maybe it is ok, but Aikido and all martial arts should go a lot deeper than that and it takes a lot longer to reach black belt
As long as they don't then go and act as if a black belt knows a lot, I don't think it really matters. It just means 'first degree black belt' will be a comparatively much more beginner rank than somewhere else. If anything, it may be a more traditional or at least more Japanese scale of ranks.
The 'Sensei' thing - well, to me their reaction seems a bit extreme but if they train with a good attitude, teach well, etc, again it's not really that important what language they use.
I would be more concerned with their actual technique and training and if you are actually interested in what they do and how they teach it - it's more likely than not completely different from what you're learning now, although if you just started you might not be far enough to have developed a strong preference. Also with the comment 'they seem a secretive bunch' - whether they are friendly and good to work with and there's a culture in the dojo you'd feel comfortable with.