What is a good monster for a lvl 60 to train on

It depends what your levels are what you are training. I will suggest a few monsters, for range and mage I will suggest monsters where you can get them from a distance and they can't get you incase your levels are low:

MELEE:
1.) I believe the best spot is in the 'Security of Stronghold' for any players from levels 30-100+.
The 'Security of Stronghold' is located at Barbarian Village. It is a hole or crack or something in the center. Go down. There are 4 different levels. Each level gets harder. Just browse through there (nothing equipped at all incase you die) until you find a good monster in there to train on.
Giant Spiders and Catablepons I believe are good for your level. But you will need food.
2.) Hill Giants are good xp also. Located south-west of the G.E. but you will need a Brass Key to enter.
3.) Guards are pretty good to train on. They aren't very strong and don't have much hp / constitution but they are very quick to kill. They are located all around Runescape but Varrock and Falador are the best places to go.

RANGE and MAGE:
1.) Security of Stronghold as listed above. You can find safe spots to attack from where nothing can attack you.
2.) Hill Giants as listed above. These also have safe spots to attack from. Big Bones sell for 450gp each.
3.) BDS (Blue Dragons) or BBDS (Baby Blue Dragons). There are safe spots here but you MUST have an Anti-Dragonfire Shield. Dragons are quite strong but VERY good cash. Dragon Bones sell for 5k each and their Hides sell for 2-3k each. Baby Dragon Bones are also about 2-3k each.
Unfortunately, you need to be a member to access this spot. If you are a member, then it is located south-west of Taverly. Go down the dungeon when you find it. Sorry, but you are going to have to use 'Google' and find your own way through.
4.) Lesser Demons. Located when you are heading to BDS and BBDS. Range / Mage from outside the wall / fence thing.

OR

There is also a non-member's Lesser Demon which is located in the 'Wizard's Tower' just south of Draynor Village. It is caged in and can ONLY be ranged and maged. Use 'Telekinetic Grab' to get the items dropped by the Lesser Demon. It cannot attack you so you won't be needing food. When you get there just climb up the ladder / stairs and the Lesser Demon should be there.

Sorry about that long message just for a simple question. Hope it helped. ;)