Just confuse them where possible.
Amazon has little idea of my age or gender.
In the past, I got DVDs to entertain the kids, when daughter went to Uni, I got textbooks for a student nurse and items of equipment she needed - torches to shine in your eyes, weird shaped scissors etc. Our son recently got trainers off it. I also got stuff for my in laws that denote some needs that are probably not in my age range yet.
The only thing they have a good handle on me for it my tasted in reading as I imagine they combine their records with Audible.com and realise that I like science fiction. Can they gauge my age by the fact that many of the authors I prefer are dead?