Didache 7:6 - "before the baptism let him that baptizeth and him that is baptized fast, and any others also who are able.
The Didache is a Catechism for adult converts. Infants aren't capable of fasting.
Didache 7:7 and thou shalt order him that is baptized to fast a day or two before.
The previous verse you posted was NOT talking about the one being baptized when it said "who are able".