"Serious Relationship" Issue.

Not often that I'm asking for help, but figured that some input would be worth it. Here goes, my apologies if its a bit long.

Backstory.
Basically I've known this girl for 8 months, we've seen eachother regularly for the last 5, and are generally good friends who get along really well. So she has been gone on a trip to Hong Kong for the past month, will be back in a few days, and while I intended to do it earlier I only confessed my crush the night before she left, it's confirmed that she has feelings for me as well and wanted to think about it over her trip.

She'll be arriving in a few days, and while I avoid talking about relationship via e-mails she mentioned briefly in her most recent one that she would want to stay friends since she's looking for a more serious relationship, and I responded that we'll talk things through when she gets back.

So, basically I'm 20 and aiming for 4 more years of studying to become a professional architect, she's 23, just graduated and is looking for a full-time job, I would consider myself to be a bit more mature than those of my age and she's got a very youthful and positive personality, so age hasn't been an issue.

What does a "serious relationship" actually mean?
I've already explained to her that Im also looking for what I consider to be a serious relationship - that it's not done because its casual or fun, to aim for the long-term and to eventually take it to the next level if it goes well.

But in this case, is it likely that she's looking for someone who's more established with work? And old enough to potentially marry in the near future? I do know that she's hoping to be married within 5 years, does it seem too early for her to consider?

Basically I'm looking for ways to deal with this issue. It means alot to me, so I'd hate to lose her simply because we're a few years apart. Any constructive input and general advice is appreciated.

i don't know lipp;

i always think that anyone who give's ANY sort of excuse not to be together it usually means that they are not all that interested and if pushed maybe they would have a relationship but it wouldn't be about chemistry and you lipp would end up losing out in the long run imo.

also she may be thinking you're just a kid compared to her.

serious means, she already wants to go out with and start planning her future with her future husband...by the fact she says she wants to be married in 5 years (bit silly and immateur to aim for that coz at what cost would she be willing to sacrifice to be married?....its possible but impossible to predict, unless she doesn't care about the person but does care more about the idea of marriage; there are plenty of women like this)

my opinion is let her go. you like her a lot more than she likes you.

just my thoughts