[zfnmxt]

It's not a wild exaggeration and it's possible for most (healthy) middle-aged men within a year (usually a lot less), except for the truly unendowed. (We don't control our genetics and/or other ailments, but I think it's better as a policy to not try to rank yourself in this regard and just be Pollyannaish about it and assume you can achieve it.)

5x5 deadlifts is generally too much volume and probably constitutes overtraining for you if they're sufficiently heavy. Admittedly, when you're not particularly strong it's less stress and more recoverable (because they can't be that heavy).

Not being able to deadlift 405 after three years is generally indicative of poor programming (if you're trying to get stronger, at least) and/or poor recovery. You have to eat, you have to sleep, and you have to increase the weight each time.