User Story:

As a Proton Calendar user,
I want to add a person's date of birth for recurring birthday reminders,
So that the calendar can automatically calculate and display the age they'll be turning each year,
And I want the option to only show ages for milestone birthdays,
So that I can easily recognize and prepare for these special occasions while maintaining privacy for regular birthdays.

Prompt for creating an interface:
Design a user interface for Proton Calendar that showcases the new birthday and milestone birthday features. The interface should include:

A monthly calendar view with a few sample birthdays, including at least one milestone birthday.
A visual indicator (such as a special icon or color) to distinguish milestone birthdays from regular birthdays.
A "Add Birthday" form or modal that allows users to input:

Name of the person
Date of birth
Option to set as a recurring annual event

Birthday events on the calendar that display the person's name and the age they'll be turning (e.g., "John's Birthday (32)").
A settings panel or modal where users can customize:

Which birthdays are considered milestones (e.g., 10, 16, 21, 30, 40, 50, 60, etc.)
Whether to display ages for all birthdays or only for milestone birthdays

A pop-up or tooltip that appears when hovering over a birthday, showing additional information (e.g., "30th Birthday - Pearl Anniversary" for milestone birthdays).
An option to set special reminders for milestone birthdays (e.g., remind 1 month in advance).
A toggle switch in the birthday event details to enable/disable age display for individual contacts.