Some of the variables may not be meaningfully continuous, such as EDU. E.g., someone with two master's degrees may have the same number of years of post-graduate education as someone with a single Ph.D.
In addition, AGE, which comes closest to being a continuous variable may not be a linear parameter if, for example, y decays as a function of age between 35-40, rises from 25-30, is stable from 40-45 and decays again from 55-60.
Residual standard error: 0.99 on 153 degrees of freedom
Multiple R-squared: 0.03106, Adjusted R-squared: -0.006937
F-statistic: 0.8174 on 6 and 153 DF, p-value: 0.558
The model is performing as specified and, therefore, works. It may not be the result desired, but that is a matter of variable selection, data selection, model selection or a combination.