I have 3 elderly - at least 10 years old ceanothus which are looking very straggly is it ok to prune them?
, it depends on the variety of your Ceanothus - whether they are evergreen or deciduous and whether they are early or late flowering. There's a comprehensive pruning guide on this RHS link:
How to grow ceanothus / RHS Gardening
You can prune them but different ceonothus benefit from slightly different timings and methods.
There is a bit more explained on the rhs site