Is it normal to be jealous of my siblings?

I'm the oldest. I have two younger sibs who are married, have great jobs, children, new cars, and own their own homes. We are all still pretty young, me the oldest being 27, and I am so proud of them for becoming such productive people. They deserve every bit of what they have and I am happy for them, for the most part. A small part of me is very jealous of them, and it makes me feel very guilty. I rent, and although I live in a nice, safe neighborhood I couldn't afford to without a roommate. I have a great job, but I make about 1/3 of what they do. I'm single, no children. The only thing I feel that I have on them is my level of education is much higher than theirs, but it burns at the same time because they went to school for less than 1 year programs and are much better off than I am. I also drive a crappy late 90's car, which doesn't really bother me because I see vehicles As commuting appliances but our other relatives do tend to poke a bit of fun at me about it. I think what I am most jealous of is the children though. I desperately want to be a parent one day but am so far away from that right now.

I feel like a horrible person for not being able to be 100% happy for them. I'd say I'm at 80%, way too low. But I can't talk to anyone in my family about how I feel because I'm afraid they will think Im a jerk, Plus none of them have been in a situation like mine (if you can call it a situation). I can't find any articles on it on the Internet or anything either, so I'm left wondering if these feelings are normal.