In world of xeen how do i revive an unconscious player?

Hmmm, heal him/her with a spell or potion.... or simply rest.

Thank you.
Is it worth joining a guild in this game?

It IS necessary to join them all.

For M&M6:
I like to get my Sorcerer up to Master Water Magic very quick, ignoring every other skill for him. Once you get to Master in Water Magic, you can choose which town to go to when you cast Town Portal, Lloyd's Beacon lasts for weeks, and you can enchant weapons. I love it!
The 2 teleportation spells become very useful later on, making it easier to perform some quests, so as to get your rep up quickly to master Light Magic.

Does somebody know how magical aging can be reversed in World of Xeen?

Tsss. I got 3 of 6 characters killed in MM1 and I have only 80 gold pieces. One resurrection costs 200.
So check after every fight (press Q) if any character is dead or not (the game show only 0 HP in a character screen compared to MM6 where the HP can go below zero).

Now can you please tell me how to increase number of spell points? I trained to level 2 but no spell points were added (MM1).

Well... keep trying :) This is the only way I know to make the SP go up. It worked for me.

I haven't played MM1 yet, but in MM2 I had to rest after training to properly update the Current / Max Spell Points of my characters. It might be the same for MM1.

SP doesn't go up until after you rest. If you've rested after training and it still hasn't gone up...then I have no idea.

Just a question. I don't get Archers. What role are they supposed to play? Are they really supposed to be good at archery, or is making them archers just a way to balance out them being fighter/mage hybrids?

I'd say in MM2 the archer is truly a ranged fighter with casting abilities. The ranged asepct is critical because in each fight only the first x characters can engage with the first x enemies. So if you have your archer in 4th position she/he can attack every round, even if only your first 2 characters are able to engage the enemy directly. My archer was easily one of my more powerful characters. In fact, towards the end of the game she was putting out more damage per hit than any other character by far.
With MM3 any character can engage in each round of combat so the ranged aspect at close quarters is moot. As a caster I generally relegated my archer to inexpensive utility spells due to lack of substantial spell points. In fact, my archer is only really useful as an additional caster that can do Lloyd's beacon. Other than that I would have been far better off with another fighter type like a barbarian, or perhaps another sorcerer. I found that I actually don't do range fighting very much because there are enough enemies that shoot or cast ranged that it is generally more efficient for me to close the distance as quickly as possible and take them down quickly in hand to hand.
I can't say for 4-6, but I'm curious to know what feedback others will have.

In MM4-5 archers are like in MM3, sorcerers with half as many mana points (casting power is the same however) but more attacks, hitpoints and useable equipment.
They don't shoot better than other characters.
It's quite the same in MM6.
In MM1 they can only cast level 1-4 spells, but get the same number of attacks as knights and paladins, unlike the other classes they can use ranged weapons in melee.

Only non-descript coordinates. I guess anything more might be considered a mild spoiler, but those should make it pretty clear to you, once you get there.
Clouds: E3 3/14
Darkside: F4 6/7.
As far as archers go, in 3-5 they're basically hybrids with a somewhat misleading name, as has been pointed out already. One thing to point out it is that their value goes up the smaller the party you play with, to the point where I'd be inclined to say they're extremely recommendable for parties with two or three characters and pretty much the best choice with no close second, if you decide to solo through World of Xeen.