Age 16 is fine in many places in the world, but for the US we coddle our children too much for them to be emotionally ready even by 18 or 19 in many cases.
The reality of the situation is that a young persons capacity for making sound judgement in terms of sexual activity varies greatly based largely on external factors relating to schooling and parenting.
For legal purposes 17 is probably a viable age for full consent, with a 2 year sliding window to accommodate 15-16 year-olds having relationships with similar aged people. This age range should be handled by families rather than be treated as matters of the state.
In this setup, you'd have no "crimes" being committed by people with a 2 year gap in age using the assumption that relationships formed between similarly aged teens are likely to be consensual. Also the idea that a horny teenager is even remotely on the same threat level as predatory person aged 20+ makes no sense, logically, scientifically or morally so punishing them for life makes no amount of reasonable sense either.