Generally, the Seireitei prefers to adopt children, babies, and eggs, and a fully-fledged shinigami will raise the little one. As stated before, teens and adults who join are considered substitutes for life. The exception is if a substitute becomes a vice captain or a captain. For example, Ichigo is a substitute. To cease to be a substitute on the same level as a shinigami in training, Ichigo would need to rise to be at least a vice captain.
Rukia's breaking the rules about bringing teens and adults into the pack to save the Seireitei, so rules are loosening. Normally, teens are trained to be a shinigami. Upon reaching adulthood, a teen joins a squad, gets the squad's number tattooed on their shoulder or hip, and gets a zanpaku-tou. All shinigami have a zanpaku-tou, regardless of rank, squad affiliation (or lack thereof, since substitutes are considered freelancers, and exiled shinigami have no official squad affiliation), etc.
A final note on the higher ranks: all dragons except the cosplays of dragons of at least a vice captain level must RP their way into the given rank. The cosplays of current captains, vice captains, and the commander will have first dibs on that rank in the Seireitei pack, to be fair, since Rukia's looking for the leaders. RP contests will periodically be held for some of the more popular cosplays, but Vizards will not be available, except through a special event Geyser and I will be hosting in conjunction with the 'Con pack. It's a plot point, sweeties, and that's when Arrancar and Espada cosplays will also be available. Arrancar, Vizard, and Espada cosplays will have stipulations on backstories and rank in the 'Con and Seireitei packs, just as a warning.
Some squads are more open to new members than others, and some squads carry requirements and such for dragons. Please be aware of this when picking which squad your dragon will join.
Squad #1: No stipulations. Captain: Yamamoto Genryuusai*; Vice Captain: Sasakibe Choujirou*; Flower: Chrysanthemum
Squad #2: No stipulations; linked for some time to the Special Ops (scouts). Captain: Soifon*; Vice Captain: ; Flower: Tulip
Squad #3: No stipulations. Captain: None; Vice Captain: Kira Izuru*; Flower: Marigold
Squad #4: Medical squad; must be led by someone with healing magic. Captain: Unohana Retsu*; Vice Captain: Isane Kotetsu*; Flower: Bellflower
Squad #5: No stipulations. Captain: None; Vice Captain: Hinamori Momo*; Flower: Lily of the Valley
Squad #6: No stipulations. Captain: Kuchiki Byakuya*; Vice Captain: Abarai Renji; Flower: Camellia
Squad #7: No stipulations. Captain: Komamura Sajin*; Vice Captain: Iba Tetsuzaemon*; Flower: Iris
Squad #8: No stipulations. Captain: Kyoraku Shunsui*; Vice Captain: Ise Nanao*; Flower: Bird of Paradise
Squad #9: Keepers of the Records (honest, I looked it up). Captain: None; Vice Captain: Hisagi Shuuhei*; Flower: Buttercup
Squad #10: No stipulations. Captain: Hitsugaya Toushirou; Vice Captain: Matsumoto Rangiku; Flower: Daffodil
Squad #11: The battle-crazy squad. Captain: Zaraki Kenpachi*; Vice Captain: Kusajishi Yachiru*; Flower: Yarrow
Squad #12: The research squad; yes, you practically have to be Doctor Frankenstein to even want to work here. Captain: Kurotsuchi Mayuri*; Vice Captain: Kurotsuchi Nemu*; Flower: Thistle
Squad #13: No stipulations. Captain: Ukitake Juushirou*; Vice Captain: None; Flower: Summer Snowflake
*Not acquired/dibbed yet.
