WHIRLWIND EXPLANATION: Pokémon have a fixed, permanent score from 0 to 31 for each stat that affects how good that stat can ever get.

This calculator will figure out that score (called a "gene" or, more obtusely, an "IV") for you, so you can discard the unworthy. It's more accurate for higher-level Pokémon, so it's helpful to go into a level 100 wifi battle with someone and check your Pokémon's stats from there.

Stat calculator

Gengar
Gengar 		Base
stats		 Stats Effort Possible genes (IVs)
Level
HP 60
231–262
16
Attack 65
135–166
impossible
Defense
−10%
 60
112–140
10
Special Attack
+10%
 130
360–394
24
Special Defense 75
155–186
18
Speed 110
288–319
impossible

Uh-oh. The set of stats you gave is totally impossible. Better double-check against your game.

The most common problem is effort; if a Pokémon has been trained at all, it'll have some effort accumulated. This affects its stats, and there's no way to know how much effort it has unless you've been keeping track. Sorry.

If you're desperate, you could try the effort-lowering berries (Pomeg et al.), which will reduce effort in a given stat by 10 at a time. Drop every stat's effort until it won't drop any further, then try again.

or start over