VFB-171-FIX: Add birth year for null age column

[minalui]

What's changed

Add birth year for rows that have null age.

Screenshots / Videos

Before	After
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Checklist

If you have made any changes to the database...

• [x] The migration files are up-to-date with my final set up (npx supabase db diff -f <name_of_migration> should create nothing at this point)
• [x] I have updated the typescript definitions for the database with db:local:generate_types
• [x] With my final set up, I can run npm run dev:reset_supabase without any errors.
• Does this require resetting the deployed database? - NO (remove as appropriate)
• [x] I have checked that migration can happen successfully without resetting the database, doing the following.
  • Make sure you have rebased your branch onto dev or merged dev into your branch.
  • Checkout the dev branch
  • Run npm run post_checkout to reset the database, including the seed data.
  • Checkout your branch
  • Run npx supabase migrations up --include-all --local to run all outstanding migration files
  • Check that the resulting database is what you expect, bar any seed data changes.