Fascias and soffits are the least interesting thing on a house and the easiest to sell badly. The fascia is the board along the roof edge that carries the gutter brackets. The soffit is the flat panel tucked underneath, closing the gap between the wall and the overhang. Between them they keep weather out of the roof space and give the guttering something to hold on to.
They fail from water, not from age. A gutter overflowing at one joint for five winters keeps that stretch permanently wet, and timber goes soft long before it looks rotten from the ground.
Repair, replace, or the whole elevation
There are three honest answers and they are very different money.
A repair is for a board that is sound apart from one soft stretch, usually under the joint that has been dripping. That section comes out, a new piece goes in, the gutter goes back on properly. It is much the cheapest of the three, and it is what most houses actually need.
A replacement is for a run that has gone along its length. New fascia, new soffit, gutter rehung, and that is most of a day on one elevation.
The whole house is the one that gets sold hardest and is needed least often. It is worth doing when the boards genuinely have gone all the way round, or when you want the lot maintenance free. Both are fair reasons. Being told your front is fine but you may as well do it while the ladders are up is not.
Which of the three yours is decides the price far more than size or height, which is why I look before I quote. The quote is free.
Ask somebody to press the timber
The only way to know is for somebody to get up and push at it. A photo from the ground shows flaking paint, which could be a board wanting a coat or a board that has gone entirely. Very different jobs, so this one is worth looking at rather than quoting off a picture.
07515 154559, Monday to Friday, 8am to 6pm. Mexborough and twenty miles, so Rotherham, Doncaster, Barnsley, Sheffield and the Dearne Valley towns in between. If the gutter above has been dripping onto the board, that wants sorting at the same time: see gutter repairs and gutter clearing. Everything else is listed under services.