It's not a bad opening, per se, but there are a lot of things that niggled at me as I read.

I am not overly fond of your title. Why, and indeed how, for example, does one affect a bilious nature? Unless you mean 'bilious' in the 'ill-tempered' sense, in which case there are countless other clearer words to choose from.

You have four sentences in this opening, one of which in particular is extremely long.

'further and farther' - is it necessary to switch between the two? Yes, there's a very slight and mooted different between the two words, but the difference here is negligible. It's like saying 'it was big and large'. Plus, since further and farther are almost identical, it looks like a typo.

'Billy’s responses seemed to so bizarre that' - seemed to be, I assume. or 'seemed to us', etc.

'he appeared completely normal' - you might get a silent objection from your reader with this. You are suggesting that autistic people are, by definition, 'abnormal', which is always a sticky situation to be in. Like if you said 'if it weren't for the wheelchair, she'd be completely normal'.

You've spent a very long time describing Billy and his non-sequitur-filled conversation, so unless you are about to jump into one such conversation, I'm not sure where you can go with this story.

I might read on for a bit, but I don't think I'm being hooked. We have an autistic person, and that's IT. I haven't heard from Billy himself, so I can't be drawn in by his character. We don't have a situation to engage me, only a slightly redundant narratorial musing. I need to see evidence of a story, and soon, or you'll lose me.

I think the prose is largely ok, it's just the way in which you're telling your story that's putting me off.

A lot of my thoughts while reading this were already pointed out by bluephoenix, and much more eloquently than I would have done.

I agree that there is a lot of description about autistic Billy...could be trimmed down a bit.

I like the first sentence about slivers of conversations. But then the move into the description of Billy was too jarring.

quote:

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Billy was not retarded at all though.

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Maybe just 2 shorter sentences describing Billy, then finish off with a grabby hook. Maybe Billy saying one of these strange responses. It could be so strange and make us wonder what Billy is really thinking that it would make us want to read on.

Just my humble suggestions, good luck.

*edited to get quote to display right