The age of consent has to start somewhere, but that doesn't mean a 15yo goes from being an immature child to a sensible mature adult overnight on their birthday. It's a gradual process and some are more mature than others - and also as PPs say, a great many 16yos aren't mature at all.
I think the age of consent at 16 does make sense as you would expect some teenagers to be experimenting with each other at that age. That doesn't mean a much older person publicly leching over a young person turning 16 is fine. And being "legal" doesn't mean there's no possibility of abuse.
I think most of us if we know someone in their 30s or 40s who was having a relationship with a 16yo, would find it icky and inappropriate, even if it is legal. Especially if it was our own 16yo!