it is quite hard to say like that so lightly "it is now, you should start.."..or opposite same...
it seems like your health is in need of some improvement, which will come certainly :)))
i think juice fasting is very very very good, and i dont see any reason why it shouldnt fit to your level or whatever you could call it...being of now :)
it is very much a matter of motivation...do yo really want to engage yourself into it?
if you do, then go for it, commit yourself to it and surely you'll get plenty of benefits!
lots of love
m