Question: why do we have baby and adult teeth?? not teen teeth? or elderly teeth? not just one set?? why do we specifically have baby and adult teeth? whats with all the teeth?!

Without wishing to appear morbid, only having two sets of teeth and the timing of those teeth is linked to the role of planned obsolescence, death, in biological systems. In nature, only having two sets of teeth effectively puts a limit on how long an individual can live. In non-human species if your teeth wear out you can’t eat, so you starve and you die. Our lives are limited and there appears to be an evolutionary benefit to this strategy. You might look at it this way – our teeth emerge and are at their best at times to help us make it to adulthood and through our reproductive years – there is an evolutionary advantage to having good teeth to that point – you’ve the greatest chance of passing on those genes that promote that ability. Genes that would allow you to have further sets of teeth after the age of reproduction might benefit you, the individual, but would not help your ability to produce the greatest number of the best adapted offspring, so would be evolutionarily irrelevant and prime for deletion, unless having good teeth into old age provided sufficient alternative advantage to the survivial and reproductive success of your children and grandchildren to offset the cost of having you compete against them for limited resources.
So, we have baby teeth and we have adult teeth but no more than these, because there’s an advantage to the species of individuals not being immortal.