Initial cleanup of ages

[gbaman]

First pass for only ages not currently in use for 2024. Goal being to remove other ages for 2026.

Removes

• 3+
• 4+
• 9+
• 13+
• 15+

As there are no workshops currently using these values.

[marksteward]

Let's revisit this after the event, there might need to be a separate field for finalised talks.