SureAI

Is there a way to de-level my character or a way to slow down the leveling? I'm a go everywhere, do everything type of player and I'm already level 21 and just started chapter two. I generally enter an area, clear all the dungeons and then move on. If the main quest can be furthered while I'm in the area, I do it. Otherwise, I just wait to further the main quest until I reach that area during explorations.

Not yet.

No wonder, this is the first time that such a mod was asked for.

I know there are several leveling mods for vanilla Oblvion, but I'm not sure if any would work with Nehrim without some heavy modification. Perhaps....

i did same, but after your level will increase very more slowly : i started chapter 2 lvl 21 i finish it lvl 28 and map monster are lvl 30-40 near the end of chapter (dark forest)

I would be interested in such a mod as well. I've been using invisibility a lot ever since hitting Cahbaet to avoid leveling so that things don't get too easy, and they're still pretty much a cakewalk.

Aside from the Steel Rail Mine and lower-level areas, the recommended levels are generally so high that by the time I reach the minimum level for an area, nothing in it poses a challenge when I explore it aside from groups of hard-hitting monsters (e.g., monsters who use the clannfear model, giants). And that's after restarting to increase the challenge by using learning points for nothing but hunting skills and other one-time-only abilities.

I'm thinking that next playthrough I'll try a thief type who uses only daggers and bows and shuns magic and see how that goes.

I don't see how you could possibly be level 21 at the start of chapter two. I just got there not an hour ago, and I'm level 7. Of course now it tells me I should be at least 11 before I continue.

You could allways try raising difficulty settings to make it harder.
I was thinking of using th CS editor to mess with starting stats, but it appears to me its not the first few levels that are easy but once you get to level 7 or 8.
It can become easy (in my opinion) because having played morrowind/oblivion for so long I have found all the quick and easy ways to make my character stronger/raise stats quick.
I have now started playing a type of character never played before and with a lot of willpower have only spammed my stats once. It is a lot more difficult and more fun (annoying that I get killed off sometimes, never did after a while in Oblivion).

I don't spam stats at all. I focus on Intelligence and Willpower every level and endurance till it reaches 50, then strength. The other stats I buff via potions or spells as needed. Like you, I've logged thousands of hours in Oblivion, so my style of gameplay is set. I like thief-mages so that's what I nearly always play. If I play a second time through, likely, I'll make sure to only kill when absolutely necessary in the dungeons. I'll skip killing anything that doesn't have either reagents or good equipment. I know I kill hundreds of rats/skeletons/etc. this game along with unnecessary kills outside.

Does Nehrim follow the similar leveling scheme as vanilla Oblivion?

what I really disliked about Vanilla Oblivion was that in order to maximize your stats you had to grind certain types of skills to certain amounts so that you would get bonus stats and whatnot. Is it the same way for this mod?

What I noticed when leveling up and allocating my stat points were +bonus points on the right side, and it seemed like they reflected the same system as Vanilla Oblivion (needing to level up your skills a lot in order to get maximum stats).

It is the same way but there is already an alternative leveling mod for Nehrim that takes care of that. Look in the mods thread or click on online mods from the Nehrim launcher.