Based on prior knowledge, we can consider the following age groups:

- Adult: typically considered as individuals between the ages of 18 and 64.
- Senior: typically considered as individuals who are 65 or older.

To analyze the relationship between the feature BMXBMI and the age group, we can compare the distribution of BMXBMI values for the two age groups.

Here is the analysis:

- For the 'Adult' age group:
    - The BMXBMI values can range from underweight to obese, but most commonly fall within the range of 18.5 to 30.
    - Typical BMXBMI values for the 'Adult' age group could be: 21.2, 25.8, 27.5, 29.3, 30.1.

- For the 'Senior' age group:
    - The BMXBMI values tend to be slightly higher compared to the 'Adult' age group, with a higher proportion falling within the overweight or obese ranges.
    - Typical BMXBMI values for the 'Senior' age group could be: 25.7, 28.4, 29.9, 31.2, 33.6.

Based on this analysis, we can create the dictionary:

```json
{
	"Adult": [21.2, 25.8, 27.5, 29.3, 30.1],
	"Senior": [25.7, 28.4, 29.9, 31.2, 33.6]
}
```