I know how you feel ... I didn't start any Martial Arts until my mid thirties, it was like being in a foreign land?
There will be many classes of immitation, without really catching the names of what the teacher is saying. It is expected in the first six months to a year, so don't get all flustered about it ... it is no big thing. Just hearing the words and seeing the techniques will become familiar friends to you as time goes on.
The quickest way to learn many of the techniques of aikido is to learn to Saguri strikes with bokken, count to five in Japanese, and not do more than your body allows.
Stretching will take longer, healing will take longer, and your mind will absorb things into a logical means of explaination rather than accepting everything at face value? Your best friends in early training will be to hang loose (feel the motion and power of technique without resisting unnaturally), using the oblique angles found in the eight point exercise for throws, and learning to use the power of your body from the hips rather than individual hands/ arms/ legs?
Still, after many years of injuries, I too must remember I am not a twentyfive year old kid, but nearly twice that today ... funny how the mind forgets until the body screams in pain? But when you start laughing because you feel the harmony of a technique, and can do it almost as well as the best person in your class can, you realize ... ten thousand more times ... and that sucker just might be mine for life!
I kind of wish I had started Aikido before forty, instead of after forty, I might actually have learned to control my anger sooner with a practice that is fun.
Enjoy your studies, and check back in a couple of months to let us know how it is going.
Oh, Yeah ... Make notes with English/ Japanese descriptions until terms become second nature. You are learning a new language.