Fix format of age tables in models

[CarolineDenis]

Fixes #5349

Checklist

• Self-review the PR after opening it to make sure the changes look good
  and self-explanatory (or properly documented)
• Add relevant issue to release milestone

Testing instructions

• go in schema config
• choose age table
• try to add uniqueness rule

[alesan99]

Testing instructions

• go in schema config
• choose age table
• try to add uniqueness rule

Works for all absolute and relative age tables 👍👍👍

[emenslin]

Testing instructions

• go in schema config

• choose age table

• try to add uniqueness rule

Works for both age tables!

[pashiav]

Testing instructions

• go in schema config
• choose age table
• try to add uniqueness rule

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Looks good!! Works as expected.