Funny how a few (20) years off Martial Arts will mess with your brain. Flexibility and fitness aside I have no problem keeping up with the other dan grades in kihon. It's not perfect but generally my stances and basic techniques have survived the mothballs. Even my Japanese seems to have been retained in some hitherto unexplored lobe. But there are two fails; the part of my brain designed to react quickly when someone does a reverse roundhouse kick to my head has shrivelled up, the body has lost control of the mind again as years of learning to step into an attack (in order to let it fly harmlessly behind you and to deliver a counter attack) has been replaced by an ape-like auto-response of:
"oh no. Big heavy foot. Head. Must Step back. Clonk" as my sparring partner easily extends their range and lands a satisfying slap.
I'm trying to take the landed blows as good-naturedly as I can despite the frustration (and embarrassment if my sparring partner is a green belt who I am meant to be helping) but for every one I get right, there are two or three where I react like a monkey.
The other brain-fart is with kata, and I've focussed a lot on kata recently because this is something I've always loved and would like to get back to competing someday. Following some success with Niseishi (it looks untidy but all the techniques are there) I wanted to nail the Pinans, Naihanchi (tekki shodan without the kicks) and Bassai. If I go really, really slowly I can perform Nidan, Shodan and Sandan the wado way and they look pretty tidy. Similarly, keeping someone else in my peripheral vision who isn't senile helps and that way I can get through almost all of them - even the dreaded Kushanku (which I think of as Kanku-dai on acid) and Seishan.
Do these same kata at full speed and I become very creative; merging katas and developing new ones. My favourite invention (and one I can't stop demonstrating) is the "get half way through Pinan Godan and finish with a bit of Bassai".