An interesting topic among various shades of psychology and sociology. The usual trend though seems to be numbers go down but quality goes up.
"Are your friends drinking/smoking? Are they underage?"
The questions a person asks tells you much about them, I suppose we have a good example here.
Anyway drinking is a fairly prominent part of the culture I find myself in, or to redo an old joke it is the only reason anybody in the UK ever has kids or gets laid (it is not but exaggeration and simplification of real things is a key part of humour and there is very much an element of truth in that).
Smoking... there have been a great many studies of smoking rates and how you might categorise people (age, location, upbringing, income levels...) within that. I am going with both more and less than you might expect. On the other hand I am old enough to have missed much of the really serious anti smoking stuff aimed at younger people (not that I have any objection -- there are so very few positives to smoking for most people and very much outweighed by the negatives) and as such I am more indifferent than some of the younger people I speak to -- it is a thing that people do, can't say the notion appeals to me but whatever they do is on them where I have met others that will treat people differently here.
Underage is also an interesting one -- 18 in the UK is the age at which you can buy as much booze as you have money for and you can buy everything from shandy to hard spirits (not sure of the rules on the really really crazy stuff like some of the absinthes out there but big boy whiskey and vodka is readily available) in supermarkets. To that end if my 19 year old friend gets slaughtered one night here I may at worst envy their good night, or laugh at their hangover, where such things have been seen to cause genuine concern in the US types I know/have observed. Likewise I am not a particular fan of age limits for anything -- statistically it can work but there are many for which it would not work or cause them to wait (assuming they care to obey said laws/guidelines) unnecessarily long.
"fade away"
The other part of being older is 10 years could go by without seeing someone and we could pick up where we left off. How often is a hugely variable thing as well, suffice it to say the "basically all the time when we are not in school" thing ends about the time you all leave school, or maybe two months later.
How many? Again we get into a classification nightmare and to make matters worse it is probably one of those many axis graphs -- there are friends that I would happily lend £50 but not £5000 and ones I would happily lend £5000 but not £50, ones I would trust to look after any pets I might have but not change a fuse in a plug and ones I would trust to build me something that would kill me if screwed up but not trust to so much as water a plant for a weekend. There are a very few people that I might clench a fist for and even do some serious evil for without hesitation and without question beyond practicality, others I might first pause to weigh the merits of clenching a fist and others still would not gain such responses. Clenching a fist is rather extreme though but there are people I might shuffle things around for, at a detriment to something else in my life*, for no reason other than I like them.
*there are very few things that truly motivate me in life, money and job advancement not being among them so if I tank a quote to instead help a friend redo something of theirs for fun then that might also be that money bores me more than any great feelings for a friend.
Are they "real"?
Imaginary friends is the domain of 5 year olds and the religious. More seriously though see above. If you mean myspace friends then I avoid all things social network so I tend to dodge that particular issue.
As for feeling lonely. I can not say it troubles me, I could see why others might and others were they put in my position might feel the same. To that end I have very little advice I can give here beyond just get out there if it bothers you -- many feel the same way.
