Why is my social security taxable income so high?

Your Social Security Wages can be higher than your wages if you have any pre-tax deductions taken out of your pay. Pre-tax deductions can include 401K contributions, health insurance premiums, FSA contributions, etc.

You do not pay income tax on pre-tax deductions, but you are still required to pay social security on these items.

Why are my 17yo sons social security wages so high when he does not contribute to 401 or anything at all?

Is box 3 more than box 1?   Ask the employer why.   There can be many reasons.   Maybe they take out health  insurance?  I never can match my husbands W2 to his paychecks.  There are many deductions that can affect it.