First things first......A mature hairline is a receding hairline. There is zero difference physiologically speaking. It just so happens that a lot men recede a small amount after which point it progresses at a snail pace, so for the sake of utility the medical sciences have labelled it as a mature hairline because yeah, the best option for people with such minor hairloss is not to even acknowledge it as hairloss and get on with their lives.
In your second last pic I feel like I can see some thinning behind the hairline. If that is not just an illusion then you are definitely looking at being effectively bald in no time at all. If not, then it is near impossible to say, you definitely have some deep recession for a 19 year old but your hair looks pretty strong overall in all other departments (aside from that one pic). At this point you should determine if there is hair loss beyond the hairline (at which point you should get on finasteride asap) or if it is simply a receding/mature hairline (at which point you should monitor your hair every few months to determine if or when it progresses).