That is totally impossible!
On Pokemon HeartGold, Moltres is on level 50.
You can get a level one hundred Pokemon in HeartGold the same way that you can get a Pokemon of that level in other games. You have to level them up until they reach it.
sentret evolves at level 20 in Pokemon heartgold
Suicune is at Level 40 in HeartGold and SoulSilver.
level 20
level 31
Level 15.
Level 30.
level 30
Level 36
Red's Pokemon levels are his level 88 Pikachu, and the rest of his Pokemon are at level 84.
56 to 63