You stop aging. You are immune to any effect that would age you, and you can't die from old age.
Boon of Immortality
RewardDMGp. 2322014
Raw data
{
"name": "Boon of Immortality",
"page": 232,
"type": "Boon",
"__prop": "reward",
"source": "DMG",
"entries": [
"You stop aging. You are immune to any effect that would age you, and you can't die from old age."
]
}