I am 29 american that started at age 20 and I direct inhale. I tried mouth inhale but my mouth must not be very big because I could never get enough smoke!
I think you will find menthol smokers tend to direct inhale and regular tends to mouth inhale.
I find that I prefer to direct inhale my True menthol and mouth the other flavours, my sister direct inhaled when she smoked menthol analogs.