As a PPL student (42 yr young) I agree that there are too many variables to accurately predict "time to first solo". I am in the circuit at current point in my training ( 10 hrs). I'm a part time student for "serious fun".
In fact, at this more cautious stage of my life I would prefer to be comfortable about going solo than rushing into it.
Many of my lessons have been cancelled due to weather often leaving weeks between lessons. In fact I reckon nothing will move out of our training centre tomorrow either. It's based in Cork (EICK), scene of todays tragic accident... RIP.