A broken watch is still right twice a day Marmalade
On EBS, I think she was chosen because she has led child abuse inquiries sensitively and effectively in the past. I find the suggestion that because she's in her 80s she isn't "top of her game" quite distasteful.
The problem with finding someone to lead any inquiry is that there are relatively few people with the neccessary skills and expertise.
Think about the kinds of skills and experience you need to have to do a controversial inquiry well. Legal expertise, witness handling, evidence examination, examining policy recommendations, working with highly emotive groups of stakeholders, coping with the tabloid press and angry politicians and campaigners. And that is just for any old inquiry - think about what something involving sex abuse needs on top of that.
And what sort of jobs develop and prove these sorts of skills and expertise? Well not very many - being a judge, possibly being a senior civil servant. The kinds of jobs which make somebody "establishment".
There are positives and negatives to it not being a serving judge. EBS's career is more or less behind her, so one risk of bias which can be ruled out is the potential fall out in terms of advancement.
Moreover, if you search hard enough (which there are plenty of journalists, bloggers, conspiracy theorists able and willing to do) you will be able to find some sort of connection on anybody which will people can use to say that they aren't impartial. Same happened to Leveson in the early days of that inquiry.
I don't mean by this that there AREN'T concerns with the inquiry OR that EBS IS the right choice to lead it, just that it isn't as straightforward as "find someone who isn't "one of them" and has no connections which could be presented as impacting upon their judgment".