Vampires are Immortal, and do not age a day from when they were turned.

Becoming a Vampire is either by choice, or accident. A pious man seeking immortality, or an Elf desiring power to rule are some scenarios that can turn one into a Vampire. Or even a Half-Orc being in the wrong place at the wrong time could turn into a night of new found immortality. No matter how one came to be a Vampire, after some time of dwelling in darkness, evil might be the easiest thing to cling to. However, with strong enough will, one could maintain their values and remain the alignment they had in life.

There is no change in your size once becoming a Vampire.

Your base walking speed is 45.

You can see in dim light within 120 feet of you as if it were bright light, and in darkness as if it were dim light. You can discern color in darkness.

If a piercing weapon made of wood is driven into the Vampires heart, the Vampire begins to desiccate and is paralyzed until the stake is removed. However, if this happens when a Vampire is at 0 hit points, they spontaneously combust and are destroyed. The soul of the Vampire leaves the burning corpse and seeks its final resting place. It may be captured and used as a component to a spell.

At 1st level, you can use your sharp fangs to inflict damage. One willing creature, or a creature that is grappled by the Vampire, incapacitated, or restrained. Hit: 2d6+DEX piercing damage plus 2d8 necrotic damage. The amount of bite damage increases as you gain levels. The target's hit point maximum is reduced by an amount equal to the necrotic damage taken, and the Vampire regains hit points equal to that. The reduction lasts until the target finishes a long rest. You may use your bonus action to drink their blood dealing 1d12 damage. This also satisfies your need for blood. A humanoid slain after being bitten, and then buried in the ground will rise the following night as a Vampire Spawn.

Starting at 5th level, your immortal nature is imbedded in your blood, making your Vampire blood able to heal any living creature by 1d20+CON.

Starting at level 3, you may sprout your vampiric wings. Although they are too weak to allow flight, you may open them to slow your fall. (As if affected by featherfall) You may also glide as you fall, allowing 5 feet of movement per 5 feet drop. Sprouting your wings can be done as a swift action, while putting them away is a standard action. 

Vampires have an unquenchable thirst for blood. While some vampires give into this carnal thirst, others are able to control their feeding habits. However, a vampire must feed, at least once, every set number of days, equal to your character level + 3. For each day after that, your character will gain one level of exhaustion. After reaching exhaustion six, this number will not rise, and you will become indefinitely paralyzed. The only way to remove this paralysis is to be given a portion of blood.

Vampires are creatures of the night, they do not belong in the sun. Although Day walkers can move and fight in the day, they are weaker than usual. In daylight or daylight effects, your speed is reduced to 25, and all d20 rolls you make have a -3 modifier. Additionally, any light based spells damage you for 1.5x damage, and may temporarily blind you for one round.

Once per short rest a vampire may become a swarm of bats, to avoid the strikes of his foes. The vampire can move up to their movement speed as a standard action. This still provokes attacks of opportunity, but the vampire is given a +3 AC bonus, and any damage dealt cannot bring the vampire below 1 hp.  

Your Charisma, Dexterity and Strength scores all increase by 2.