Based on prior knowledge, blood insulin levels tend to increase with age. Therefore, it is expected that senior individuals would have higher blood insulin levels compared to non-seniors.

Here is the dictionary with the possible values of feature LBXIN for each target class:

```json
{
  "Adult": [5.2, 6.1, 7.5, 8.3, 9.0], 
  "Senior": [10.7, 12.4, 14.9, 16.2, 18.8]
}
```

In this dictionary, the "Adult" class represents non-seniors, and the "Senior" class represents senior individuals. The provided values are hypothetical examples of blood insulin levels for each class.

Please note that the values provided are not exhaustive and are only meant to demonstrate the format of the dictionary. In a real analysis, a more in-depth exploration of the relationship between the feature and target classes would be necessary to determine the appropriate ranges of values.