Do you mean you are afraid to get married to her, because of the age difference? Or you are afraid of what US Immigration will think of the marriage?
If it's the first, don't get married to her. If it's the second, get married but wait until 2 years of marriage before filing for the green card (I presume with your "high income" you already have a work visa so you can stay for a while without her filing anything for you). Once you pass the 2-year mark, it is much easier to convince the authorities of the validity of the marriage, and you'll get an unconditional 10-year card when approved, instead of a 2-year conditional card that requires you to redo paperwork (and possibly re-interview) 2 years later when it expires.