Should I evolve my Grovyle?

The only real reason to keep a Pokemon unevolved nowadays is if a different play-style is desired (as with drastic changes such as Scyther and Scizor), or if the defenses would benefit enough with an Eviolite (such as with Dusclops and Dusknoir). However, Grovyle and Sceptile play similar (being part of a three-chain evolution), so the first case is not valid. Neither Pokemon are defensively based anyway, so an Eviolite doesn't benefit enough to create a need to not evolve.

With that being said, EV training will occur in ALL compotent competitive opponents. This isn't debatable, this is how it actually happens. Your opponents will be doing whatever it takes to legally get their stats to the maximum, so letting them have any lead on you is another step towards their victory. The assumption that EV training will cover for the lose in base stat isn't valid; Sceptile would get all benefits that the Grovyle would get from EV training and use them better.

Your timing isn't pressured though, you can evolve it late and get the same stats as you would at the same level evolved a dozen levels before. Use this benefit to learn desired attacks at earlier levels (typically, the lower stage evolutions will learn moves earlier than their evolved counterparts, while some learn attacks their evolutions can't learn!), so if you plan on evolving it, be sure to do so when the Pokemon's moveset is ready for evolution. That's not to say that evolution finalizes the moveset, but I'm suggesting you take every desired opportunity to snag whatever needed move at the earliest opportunity. This way, the preparation of the Pokemon will take less time. If you have all of the moves you want for it already, then evolve it when you feel ready, but don't slack off on evolving it.

If you want to play competitive with this evolutionary line, I'd recommend you evolve it. The sad truth is that you don't use this particular evolutionary line to its full advantage unless you evolve it to its most powerful and statistically more suitable form (the higher Speed and higher attacks Sceptile). The sadder truth is that you may have to swap this Pokemon with one that is better suited for your team (such as a Venusaur) if needed in the long run. Believe me, that stings, but that's part of the cruel competitive world. If you can make it work though, be it building a team around Sceptile or using it to fill a niche or role, then use it to its fullest and use it wisely.

What Level Does Grovyle Evolve

Sceptile has better base stats than Grovyle, so if you plan on battling competitively with it, then it is wise to evolve it. You can EV train the Grovyle to make it stronger, but its stats will also change accordingly when you evolve it, (meaning that it will gain its base stats and still keep the EVs.) As long as you evolve it before level 100, though, it will keep its same stats as it normally would, (meaning if you evolved it at level 50, it would have the same stats by the time you evolve it by level 99.)

Grovyle

At level 36!

Honestly it's a personal choice but Sceptile is better and you might have better luck with it. But if you really like Grovyle stick with him.

if you want to win use Sceptile