Based on my prior knowledge and common age groups, I can make the following assumptions about the relationship between the feature RIDAGEYR and the task of predicting the age group:

- I will consider the age of 65 and above as the threshold to classify someone as a senior. Anyone below 65 will be classified as an adult.

With this assumption, I can analyze the relationship between the feature RIDAGEYR and the target variable. Here's the dictionary with the details:

```json
{
	"Adult": [18.0, 35.0, 45.0, 50.0, 60.0],
	"Senior": [65.0, 70.0, 75.0, 80.0, 90.0]
}
```

These are typical RIDAGEYR values for each target class. The values [18.0, 35.0, 45.0, 50.0, 60.0] represent ages of adults, and the values [65.0, 70.0, 75.0, 80.0, 90.0] represent ages of seniors.