I was wondering if the ABRSM piano exam is open for adults as well?
Yes. Anyone of any age may take the exams.
For those who have taken it, what is it like exactly? Do you submit a recording of one of the pieces or do you play in person front of a judge/scorer?
You play for an adjunctor. You do what is listed in the syllabus for them.http://www.abrsm.org/regions/fileadmin/user_upload/syllabuses/pianoSyllabusComplete13.pdf
Play your technique (they will select something from the syllabus - you are responsible for it all but expected to only play a bit)
Play your songs
Play a sight-reading exercise
Do the aural exam
Right now I am self studying Alfred adult book 1, at what point will I have covered the requisite material for the Grade 1 exam?
Alfred book 1 never approaches ABRSM Grade 1. I would think the end of Alfred book 2 would be approaching it, but still not quite there. However, the 'problem' with ABRSM is the extreme limitation of pieces you can choose from for the exam.
Take a look at the syllabus and see if you can play any of those pieces. Also, an exam is probably better done if you have a teacher. You should really only take it if you feel that you need it. Otherwise, spend your time doing other things.
I'd follow this if I were you and looking to do classical piano: http://www.theachievementprogram.org/sit...2012_SECURE.pdf
This has FAR more pieces at every level. It may be more suited to you, depending on your goals and current abilities.