I feel like im slightly qualified to answer this so I hopefully this helps and i apologize for my essay!
mt little back story: I meet my SO online (reddit actually) we hit it off straight away and pretty much Skype'd nonstop, at first i was ashamed of my age, I was 19F, he was 33M. I thought if i told him he would not want to talk to me as the age gap was too much, ended up telling him on my 20th birthday my age and he was cool with it We both live in Europe but in different countries, I'm English and he luckily speaks Amazing English and I too have started learning his language.
So heres my answer to some of your questions:
The distance sucks we don't have a big time difference but not being able to see each other whenever we want sucks to the highest degree. Though i try and look at it on the bright side, I get to be independent on my day to day life, but still get to come home and have someone who will listen to all my problems.
as for Closing the gap /r/longdistance has a lot of people in LDR's who have been in them for years, they have great advice and a wonderful support network. yes wanting to close the gap is natural but it may not happen tomorrow, next year or in 3 years, have a game plan, know when your gonna see each other next and focus on that. Focus on your studies, don't rush into any relationship and keep yourself safe just incase this all goes tits up (like any relationship) you still have an education and job to fall back on (maybe look at becoming an English Language teacher, you can travel anywhere with it and live in his contry with a good job)
Now for the juicy bit the age gap loud disapproving gasp 10 years is a big age gap, there will be differences.
He will be starting to have friends and family settle down and getting married and having kids and he may want to also do this sooner then later, having a discussion with him about this is always good, i told my SO my lowest limit of starting a family and I whole to stick with it, the positive is that you are the woman and younger, you have no ticking womb clock begging you to get pregnant.
You will be struggling with your parents not giving you space to mature or University/Friends and he will be worried about Bills and job promotions, though anyone can experience these problems at any age being a young woman means (and I may just be speaking for myself) there is more drama in it all. The fact that Rachael didn't invite you to her house party may be the most devastating thing to happen to your friendship, he'll possibly have more stable friends where things like this aren't a problem and find your worry's completely inane. Though if your lucky like me he'll still listen and give advice, just keep in mind that the problems you may face will be different and try and just support each other in what ever you face.
Finally how other people react, you can already see from how people on here have reacted that there are few happy banners of joy and rainbows but that's okay. These people, be it strangers on the internet like myself, your best friend or your parents, they are not in your relationship. They will have opinions and try and tell you what to do but its not there relationship, its yours and your SO's and that's what should matter, make each other happy. Let others see how happy you make each other and hopefully they will understand that an age gap is nothing more then a couple numbers on a piece of paper
Don't be ashamed of your relationship, if you are then how can you give it love, attention and time to grow, be open and honest with people, don't shove it in there faces but at the same time allow them to ask questions its a different kind of relationship people will be taken aback by it and want to know why the hell an 18 and a 28 year old would possibly want to be together because they sure as hell could never see themselves with someone X amount of years younger/older then them, which is fine but you do and you are happy.
I think my SO is wonderful and appreciate him more and more for the kind and caring man he his, people know about him and have there negative and positive opinions, my family are still getting used to the idea of him but they can see how much happier and more confident in myself I am and are trying to keep an open mind and that's all I can ever ask of them
Best of luck to you and your SO!!