Based on prior knowledge, we can analyze the relationship between the feature "BMXBMI" and the task of predicting the person's age group (Senior or non-senior).

Typically, older adults tend to have higher body mass index (BMI) values compared to younger adults. However, there isn't a clear cutoff point for differentiating between senior and non-senior age groups based on BMI alone. 

To create the dictionary with specific details, let's assume the following ranges:
- Senior: BMI > 24 (overweight or obese)
- Adult: BMI <= 24 (normal or underweight)

Based on this assumption, we can generate the dictionary as follows:

```json
{
	"Adult": [18.5, 20.0, 22.3, 23.8, 24.0],
	"Senior": [25.5, 27.9, 28.6, 30.2, 32.1]
}
```

Please note that these specific BMXBMI values are just examples and may vary depending on the dataset and the actual relationship between BMI and age groups.