How many carbons does an alkane need to have an enantiomer? How many carbon atoms does an alkane need before it is capable of existing in enantiomeric forms?
If we allow our substituents to be isotopes, then 2 is all that is really necessary:

$\hspace{6cm}$

If we exclude such compounds from consideration, then cyclopropanes will give you smallest number of carbons at 5:

$\hspace{5.5cm}$



As a side note, for a non-alkane, only 1 carbon is necessary:

$\hspace{5.7cm}$