The appropriatness of having sex is different for everyone, here in the UK it is illegal to have sex with anyone under the age of 16, so it would not be appropriate for anyone to have sex under the age of 16, as it would be outside what our government accepts as normal, therefore not appropriate.
However your extended questions asks about age and morality which isvery much an individual process. I was 15 and 9 months (so not so far off the legal age) and I felt ready morally, spiritually etc… Whether or not that was appropriate will differ with each one of you.
There are so many unwanted pregnancies, not just with young people, so is age a major issue? My sister had her baby at 17 she used a condom and took the morning after pill but still ended up pregnant, she was fortunate enough to have a very supportive family and although it has been difficult at times it was the making of her as she could have ended up down a very different path. So for her sex and preganacy at young age has done her a favour! (I admit this is not the case with lots of others and by no means recommend young people go out and have sex willy nilly, I was just playing devils advocate and using my sis as an example)
As long as you are safe in both choice of partner (possibly adding legal age into the equation too) and using a condom then why not?
Sex is a natural instinct and no one will ever stop it from happening. In an ideal world no one would have sex until the legal age there would be no STD’s and unwanted or unexpected pregnacies this is never going to happen so we just have to make sure younger generation are aware of risks both health and pregnancies and hope that somewhere along the lines these messages sink in.