By RAW, no. The don't have the ki pool class feature yet, which they don't have. So they can't choose to take the feat.
However, I can't see any big problem in allowing them to do so anyway, it isn't a really strong feat choice that needs only to be availiable at higher levels. Let them take, even though they can't use it before they actually get a ki pool.
The feat itself would not be waisted. You would just have to wait until you actually meet the prerequisites to gain the feat's benefit. If you really wish to go this route, then I would suggest taking Extra Ki at 3rd level. As soon as you hit 4th, you will have some extra ki ready to rock!