Are there any rescues near you? It can be helpful to go to a rescue as you tend to know what the rabbit will be like personality wise. Most rescues are adults and spayed or neutered. Some rescues can help you with bonding and the rabbits can meet before you adopt.
If you don't have a rescue close by, I would still suggest trying to find an adult. Even 6 months is considered adult, so they don't have to be too old. Again, adults tend to be more set in their personality, so you know what you are getting. It can be hard if the rabbit isn't altered yet, but most do calm down once that is done.
Babies can be hard to tell what they will be like. Usually, if they are very active, they tend to be active as adult. A laid back baby may stay calmer, but you do need to make sure it is just calm and not sick.
It can be hard to judge based on breed. Some breeds are more known for being laid back, and other for being active, but there can be individuals who don't fit in with those ideals.