My experience has been essentially what redshepherd suggests: The longer you wait, the more difficult it is to switch them over in my experience. However, your snake is pretty young and this observation mainly applies to adult animals (i.e. 2-3+ years old). You could easily feed him live food 5-10 more times (between 1-3 months) and be pretty confident in still being able to switch him over. 58g is really tiny for a 4 month older snake, so I would join the others in their advice to get some size on him.
Ideally, I would get both a F/T and a live and try the F/T, if he takes it, great. If not, you have a backup. This is more expensive, but with frozen rats being pretty cheap these days and you'd only be doing this for a short period of time, you'd likely save money in the long run (by getting him to F/T asap).