Absolutely love visiting Coniston Old Man - but it can get very busy, well worth exploring the other fells surrounding it if you'd like more peace and quiet. There are sections where dogs can safely be off-lead, but there can be sheep around and you need to be mindful of other walkers and dogs.
Loads of different routes to choose from, and the main one is a fairly established path, so as long as you have a map and are properly dressed and equipped you should be fine, but just be aware, this is a mountain walk and the weather can change quickly and it's easy to become lost if the cloud comes down - so plan carefully and be prepared for this!