[PennysMum]

As long as your older boy isn't fat, there's no real reason to worry about switching him now. Puppy diets usually have more fat and often have higher protein content than adult foods, and many small breed dogs can actually benefit from that due to their faster metabolisms. If he starts packing on the pounds at some point, switch him off the puppy diet-- otherwise, I'd say it is perfectly all right for him to stay on it until the other puppy is older.