My first level 100 Pokemon was Blastoise in Red. I can't remember how long it took me to get him there. It felt like a long time, but since I soloed the game with Blastoise, I doubt it actually took all that long. I recall some other kids I knew telling me that Pokemon would die upon reaching level 100, so I was really worried about getting my Blastoise there. Needless to say, I decided to test out the level up at the Elite Four, planning to reset the game if my Blastoise died. Apparently, I didn't know about the game's autosave after beating the Elite Four, so if reaching level 100 really had killed my Blastoise, I would have been in trouble. Obviously, reaching level 100 didn't actually cause any harm, and made me one of the first people I knew to have a level 100 Pokemon, so in the end, I was quite proud of the accomplishment.