Instead, create a custom Age group entity and synonyms for each individual age in the corresponding item.
Use Age group for Identify in the question.
The prebuilt entities cover commonly used information types, but on some occasions, such as when building a bot that serves a specific purpose, you'll need to teach the bot's language understanding model some domain- specific knowledge.
To do this, you need to create a custom entity.
Reference:
https://docs.microsoft.com/en-us/power-virtual-agents/advanced-entities-slot-filling