Your Constitution increases by 2; your Dexterity increases by 1.

Dullahan don't have ages. They are simple born with the apparent age they will have for the rest of their "immortal" lives, since they can't die from old age.

 Dullahan are primarily neutral as agents of death.

Dullahan  vary widely in height and build, from barely 5 feet to well over 6 feet tall. Regardless of your position in that range, your size is Medium.

Your base walking speed is 30 feet.

Your head has Darkvision with a range of 60 feet, even when detached.

 Dullahan fear gold in any form. You cannot carry gold and any form, and you grow nervous when in close proximity of gold. The preferred method of payment for most Dullahan is with gemstones or magical items.

You can remove your head without harm, and your head can still speak even when detached. Without your head, your body has blindsight with a range of 20 feet. If you take damage from a critical hit, your head is literally knocked off of your shoulders, and lands somewhere on the ground 5 feet away from your body. During your turn, whenever you move to the same space as your head, you may spend your bonus action to retrieve it.

 Every Dullahan has a "familiar" in the form of a jet black horse, which has a striking familiarity with a Nightmare with black smoke instead of flames. You can summon your steed with a bonus action. The steed has the same stats of a Nightmare, with the exceptions of the "Confer Fire Resistance", "Illumination" and "Ethereal Stride" feats, and it also doesn't have a flight speed. At level 10 the stead has the ability to take the Dullahan to the Fey Wild once every week. You also gain proficiency with the "Animal Handling" skill.

You can speak, read, and write Common and Abyssal.

You have advantage on saving throws against being charmed, and magic can’t put you to sleep.