At that age and still now I feed when she grizzles - essentially demand feeding. I don't take sucking on hands or anything really as a feeding cue, like Flutterby, I have learnt the sound she makes when shes hungry. Sometimes we go 1 hr between feeds, occasionally 4 hours (she usually feeds for 5 mins or so). Personally, I have found it much easier and less stressful to let baby lead. So at 6.5mths she feeds roughly 6-7 times per day sometimes more if shes teething and not feeling the best and extra at night if she wakes.
In answer to your question 'how often should he be feeding', I guess it depends whether you want to continue demand feeding or schedule his feeds. Really depends on what works for you and your little man
Edited to clarify myself

Hopefully it makes some sense!
Edited by Mamma2N