Based on prior knowledge, we can analyze the relationship between the feature BMXBMI and the target task of predicting age group (Senior or non-senior). Body Mass Index (BMI) is a measure of body fat based on an individual's weight and height. 

Typically, below 18.5 is considered underweight, 18.5 to 24.9 is considered normal weight, 25.0 to 29.9 is considered overweight, and 30.0 or above is considered obese. 

Based on this analysis, we can assume the following ranges for the feature BMXBMI to predict the age group:

- Senior: BMXBMI values above 30.0
- Adult (non-senior): BMXBMI values below or equal to 30.0

Using this information, we can create a dictionary as follows:

```json
{
    "Adult": [18.5, 23.7, 27.8, 29.4, 28.1],
    "Senior": [35.2, 31.8, 39.0, 32.5, 33.9]
}
```

Please note that these BMXBMI values are just examples and are not exhaustive. The actual values will depend on the data and analysis conducted.