Is it possible for a bike tyre wear at 18000 km ?

i am using a splender bike.at beginning, my front tyre had very good traction and would respond well at sudden brakes even at high speeds.but for past few months, it is starting to skid when brakes are applied even at low speeds. it may look obvious that it is because of tyre wear but i am not 100% sure of it.because a tyre will last upto 40000km but mine has just covered half the distance.next is, my tyre doesnt look has if it is having much wear.i mainly want to know the reasons which can lead to pre-mature wear of tyres. and i like to mention the fact that i didnt regularly set proper air pressure in tyres for last 3 years.is that the only cause for pre-mature wear or is there any possible reasons other than this