The thing is, readiness for sex is a matter of maturity rather than just age. There are people that would be perfectly ready and emotionally mature enough for sex at age 14, and there are people that are still a bit too immature at 18 and beyond. Therefore any age-based line we set is going to appear arbitrary, but I'd prefer that it was higher to protect people below that age that aren't really ready, at the slight expense of stopping people who are ready below that age from having sex (although only in a legal sense - they're probably gonna do it anyway!). 16 is fine, IMO.