The concept of providing tax breaks for senior citizens based solely on income is seriously flawed. Many seniors have little "income" but lots of resources that make up their net worth. To allow these wealthy (in terms of net worth) seniors to push the burden of paying taxes to younger taxpayers who are trying to build their net worth from relatively higher incomes while raising their kids, paying off their mortgages, spending inordinate amounts of time in traffic, etc. is totally unfair.
Before considering this kind of legislation, there must be some consideration of the totality of a person's (or couple's) assets including income (e.g. pensions and Social Security as well as salary) but also other assets (including 401(k), paid off house, stocks, bonds, etc.) The fact that we have no way to find a U.S. tax form to substantiate this value does not obviate the need to do so. It just means that we can not categorize seniors solely on the basis of income and pass legislation such as this.