Thanks to all for the helpful replies. It is encouraging that others with back problems have been able to manage this issue and maintain aikido practice.

I also heed the advice to be careful. Three or four years ago I couldn't have contemplated this but with the improvement I have had in the last couple of years I think it is a realistic possibility. I appreciate that a careful approach is in order and would certainly have a discussion about this with the instructor should I go ahead.

One of the dojos I am considering has most of the training sessions in the early morning (ie 6:30am!). This may be an advantage since it would minimize the amount of interference with family life (eg helping the kids with homework in the evenings) but I do wonder if it would be okay from the point of view that you tend to be a bit stiff in the morning and the back more vulnerable.