"I'm going to do..." = my choice "I'm going to wait and ask him first before I do it." "No.. I'm sure it's ok.. let's just go ahead (decide without asking him) and do it"

Good day; To "go ahead" generally infers that one has been waiting to do something. But not always. For example; :We haven't heard from Tommy yet, so I'm going to go ahead and start dinner." Or. "I'm still waiting for Jolita to arrive but I'm going to pour the hot water, for tea, anyways. We'll pour her a cup when she arrives." However, some people simply use it to liven up their conversation. It's time to meet the school bus and I might just say "I'm going to go ahead to the bus stop now." I hope this helps, Stephen