It's hard to say. I personally don't think it's an issue, especially if the guy is an absolute gentlemen and people have never met him. However, everyone has flaws - including the absolute gentlemen. Yes, the 26 year old has more life experience than you do. But I'm not sure 8 years is that much of a difference.
I wouldn't like it if it were my little sister or something. But realistically at 18 anybody is allowed to make their own decisions. If it's a mistake, it's a mistake, it happens, and mistakes are usually good learning curves.
I can see problems at a mindset level - You are at probably at different stages of your life with different aims in life at the moment - On whether he will try to take an advantage of you, I would say that is a question about him as an individual as opposed to what age he is - An 18 year old could try to do that as well.
Goodness ! That's ages apart like "wow" but that's not a bad thing because you're legal. But are you willing to handle the responsibility of being with a guy who perhaps may be very mature and are you willing to do the grown things he's intended to do? I'm not saying "sex" but you have to really be mentally ready for that. Not every older guy takes advantage of someone who is younger than them. I believe it's a good thing because depending on the guy he is mature and willing to accept responsibilities but personality varies and it all depends on the type of guy you're dealing with.
You date who you want to date, 8 years can be a lot but it depends on if you're ok with it and if he's a decent guy. Just be cautious, don't get talked into doing anything you don't want to do. You can be manipulated by a guy much older than you at your age now, that of course is possible but you're also legal, so you're free to make your own decisions. I'm dating someone 12 years older than me, so just be careful but do what you want at the end of the day.
You're of legal age, you can make your own decisions. At least he's not 40. Like that age gap isn't a problem, and really it isn't anyone else's relationship, so their opinions don't matter. If you like/love someone, don't let others opinions prevent you from being with them. Screw the judgmental people.
Quit giving a crap about what other people tell you. It's your love life, others should have no say in it. If you like him and he likes you, and you think it could work out, then give it a shot! The age difference isn't even that big, I know a woman who is happily married to a man 17 years older than her.