Silent Courting: How do you know if someone likes you?

I met my friend for lunch this week and we got to discussing work, clothes and worked our way into dating or lack of in our lives. Placing her sandwich down, meticulously arranging it on her plate,she paused a while.Judging from her carefully controlled movements, I knew she had something of import to divulge. We have been friends for a while and in our years of friendships we have come to read each other's tell tale signs.

Settling back on my seat, I took a sip of water and waited for her to speak. With a serious deadpan face, she announced softly" I am ready to get married!". That definitely caught me by surprise!. I did not even know she was dating anyone much less discussing marriage. Doing a fine impression of goldfish I intelligently uttered" well!... oh... well!".

Still in a serious tone she looked at me and said" I don't know if he is the one but I like him". Snapping out of shock, I smiled at her " If you like him, then the major part of the battle is over!. so why the doubts?".
" well, he is younger than me".
Here was the tricky part.From being youngest in the group, we have slowly progressed to become not that young to this fine state.Fantastic quotes of age raced through my mind but before I could impart my pearls of wisdom, I wanted to make sure of the age gap. It could be Demi/Ashton or minor. One would need to come with the ideal response or it may blow up in your face. Keeping that in mind I asked cautiously" Under 5?"
" No"
That was no help!.
I prodded" Under 10 years?"
"Yes"
well we were getting somewhere!.
" He is 8 years younger"
"That is not so bad, I would have told you to think twice if he was ten years younger or more, since he'd be in a different generation and all. but 8? phoo..phoo!! that is nothing!. I'd say, in maturity, you would be just about even!. yesssire..this is nothing to worry about!"
she shrugged.
o.k., I guess there is more" so what is the other hindrance?"
She toyed with her water glass, then looked at me and said" I am not sure about his feelings. He treats me as if I am younger than him. He teases me and we have a good time when we hang out together. I am very comfortable with him, but I don't know if he considers me as his pal or girlfriend and I am so afraid to find out! what should I do?"
Normally, it would be so easy for me to pump up my friend and would be quoting " Carpe Diem",until I was blue in the face, but this was not just anybody. This is my friend, who would break if she took the leap only to fall flat on her face. Besides, she would have to see him after that, as they attended the same social group. It would be an excruciatingly painful embarrassment!.
I had no advise for her!. What does one do? How can you tell if someone likes you?. How can you tell apart the various forms of liking?. I obviously did not have a clue!. so I did the next best thing, I empathized with her and mouthed platitudes.