I disagree with Bike Nerd on a number of points.
First, I think everyone should learn on a hardtail, you’re cheating yourself out of valuable and necessary skills by jumping straight to a full suspension bikes – they do a lot of the work for you and while, yes, I ride a full suspension, there’s a lot of value to be gained from riding a hardtail, and I still enjoy riding hardtails now.
Full suspension is not necessarily ‘more fun’, it’s just different.
Also I disagree on his point regarding wheel size. I’m 6ft tall and prefer 27.5″ wheels. That’s just my preference. Try a few bikes and figure out which wheel size you like. The notion that 29″ wheels are for tall people and that folks our height shouldn’t be riding smaller wheels is a fallacy.
I do agree however that going used is a good idea. His point that you stand to spend more than you need to by buying new is fair. I think it is useful to buy a cheaper bike to learn on – you don’t want to spend too much on your first bike as you’ll likely crash it a lot. Buy a used hardtail and you don’t stand to lose much money when you inevitably upgrade – then buy something nice and new once you know what you want, so you can take care of it and have a good warranty.
Good luck!