It depends on what you mean.
Any age dog is trainable. If you're talking about teaching the dog to perform behaviors on command, you haven't lost anything by starting at 8 months rather than 2. If anything, the dog will probably be way easier to train at this age. Little puppies are dumb babies.
If you're talking about socialization, yes, some of the windows have closed for early exposure to certain things - other animals, strangers, weird stimuli, etc. But older dogs can still be conditioned (and counter-conditioned). And temperament is mostly genetic, anyway, which largely governs how the dog reacts to other animals, people, etc. regardless of how socializing was conducted.
If you're talking about training of good habits, like crate training, not jumping up, not being a pest when the family is having mealtime, etc, IMO yes, that area is easier with a "blank slate" little puppy than an older dog that might have picked up some bad habits. On the other hand, 8 months is not very old at all and again, all those issues are correctable, it just requires more effort if the dog needs to unlearn a bad habit. Probably the bigger challenge you'll have in this area is that in my experience around this age the dog is heading into adolescence and starting to feel his oats. This would have happened regardless of whether you'd gotten him at age 8 weeks or now, it's just that you haven't had the opportunity to become fond of him as a cute little tiny puppy before getting his teenage sass.
FWIW I adopted a literally feral 1 year old dog and she ended up being a fantastic housedog and friend after some time and effort. She lived to be 17 and traveled all over North America with me. Dogs are genetically programmed to work with humans.
All in all, as cute as puppies are, IMO most dogs don't really get particularly fun to work and live with until they're 18+ months old, so I'd consider adopting an 8 month old an overall pro (versus adopting a younger puppy) as you're getting to skip past a lot of pooping, gnawing, and whining.