I would go for the older house.
But will you be able to get planning permission for the extension?
Have a look around the area and see if other similar houses have new extensions.
to be honest, i don't think you could get the plans drawn up, planning submitted and then built (assuming no extra info required from council during the planning process) in seven months.
iirc the council have to make a decision within eight weeks after the plans are submitted.
the old house sounds lovely, it would definitely be my choice, but would it matter if it took longer than the seven months?
could you rent near this house while renovating?