I hered that the level for first gen Pokemon can be higher than 100... something like 152 or 252... I don't rember what it was, but is it true the levels were able to exede 100 in first gen, or is this false? If it is true, what was the highest level?
By exploiting the old man glitch in Generation I, a Pokémon can be acquired at a level higher than 100. Also in Generation I, any Pokémon can also be raised to a level above 100 via the Pokémon merge glitch; however, Pokémon in the Slow experience group need to be merged with a glitch Pokémon who requires even more experience at level 100. These Pokémon can continue to be leveled up with Rare Candies until level 255. Whenever a Pokémon over level 100 gains any amount of experience, its level will revert to 100, and if a Rare Candy is fed to a level 255 Pokémon, it will revert to level 0.
So, yes, a Pokemon can exceed level 100 in gen I and the highest level a Pokemon could be is 255.
Source: http://bulbapedia.bulbagarden.net/wiki/Level
In every single game, the highest level a Pokemon can become is 100. This includes the first gen. However, doing the missingno glitch (which can be found here) and surfing on the water that missingno appears in can sometimes result in finding random Pokemon about lv 100. For example, a lv 152 wartortle can appear. These are glitches though, and by normally leveling up, they can't exceed lv 100.
Yay! I found it! :D
According to bulbapedia...
In Generation I, it is possible to encounter and catch Pokémon at levels over 100 through the old man glitch, and encounter them in glitch Trainers' parties through the Mew glitch.
-Bulbapedia
The link is for helps, and for future references.
I'll just send the link here.
