It really depends on the individuals state of health, fitness level and body weight.
I'm lazy. I don't train really. I'm 66.
As a Camino date starts approaching I do two things.
- Reduce my bodyweight. I'm normally quite overweight (10-12 kg or so) so this gives me an incentive to lose some weight. I know if I don't that the Camino is going to hurt! So I aim to get my BMI into the upper range of 'normal'. Actually, lower range of overweight, just checked. I'm normally about 32 and aim for 27 or below. Maybe next time I'll try to get to 25!
- I walk a bit. Nothing much really. Some easy walks on a soft surface, around local parks, hiking trails. Maybe building up to 20 kms / week.
But......
I also start slow on the Camino. I build up my distances in the early days, to my comfort level of 20-25 kms / day. For example in the first days on the Camino I might walk 10 kms, 14 kms, 18 kms, 20 kms and so on. Just to warm up. By day 5 or so I'm at my planned daily distance.
If I planned to start out at those distances, I would walk more at home prior to the Camino.
I could claim that work and other commitments preclude any serious training, but the truth is, walking at home bores the pants off me I love walking on Camino, but really have no interest to do it elsewhere.
I don't even train with a full weight pack, because it might cause injury in training.
I wish I was more inclined to train, but I'm not. I just know with excess bodyweight gone and some light walking beforehand, along with a gradual build up on Camino I'll be fine.
I managed a 1200 km Camino OK this year....... No drama, no injury.
But I'm not recommending my approach!!!
Just offering another perspective.
But for a first Camino........I'd train a bit.
Though be careful to not overtrain. I did and still carry the injuries 8 years later.
Maybe that's why I hate or maybe 'fear' training