Adam Clarke on Job 30:1

But now they that are younger than I have me in derision - Compare this with Job 29:8, where he speaks of the respect he had from the youth while in the days of his prosperity. Now he is no longer affluent, and they are no longer respectful.

Dogs of my flock - Persons who were not deemed sufficiently respectable to be trusted with the care of those dogs which were the guardians of my flocks. Not confidential enough to be made shepherds, ass-keepers, or camel-drivers; nor even to have the care of the dogs by which the flocks were guarded. This saying is what we call an expression of sovereign contempt.