I believe he is at level 45, but it might be 40.
you can't find Groudon
At ruby version Groudon is level 45, at emerald Groudon is level 70.
Groudon is on level 50.
We cant get a hundred level groudon but we can get a ghostly groudon in the cave in the downright part of the page
Groudon can learn Solar Beam at level 50.
Groudon can learn TM28- Dig.
You get Groudon in Pokemon Heart Gold by trading with somebody who's found Groudon in Soul Silver. You can't find Groudon in Heart Gold, you find Kyogre. Soul Silver players find Groudon.
at level 50.
Migrate a level 100 groudon to diamond, pearl or platinum then go to the pal park and then you will find it in the park throw a park ball to catch it.
magma cavern
40
There is no Groudon in Pokémon Crystal.