Almost two weeks has passed, no answer in sight, so I might as well give one.
In short -- yes, you can do that.
A more lengthy one goes below.

Just go into the settings in game's main menu, then choose "game". There you would need to change "population cap" from original 200 to 6 (or 7, if you meant to play with dwarves that you start with and not literally with 6) and also change "strict population cap <includes births>" from 220 to somewhere around 12 or 14. The first change would prevent migrant waves from happening' and the second one would make would make sure that your fortress won't became a massive kindergarten, wich by itself is not guaranteed, but can ocure sometimes.

If you don't want your dwarves to have children or want somethin' more concrete for them before they do so, then change " baby+child cap" from 100 to 0. That will prevent any children from ever existin'. And\if you will start too feel that it's finally time for your dwarves to have a proper social unit, then change it to 3 or whatever you feel right. The aforementioned social units is not guranteed however, since they simply may be not into each other and you can't do much about it, apart from makin' sure that they don't have opposin' values in "prepare carefully" thing and havin' enough leisure time for them to actually socialize.

About socializin': if you would like to make your tavern, which is bein' an important part of dwarven culture and havin' a non-negotiable existence at any fortress, open for visitors, then "visitor cap" should be changed too. 5 or 6 should be enough. Or don't change it if you want it to revolve around your tavern. It's actually very atmospheric if you dig into the cavern layer first, because then monster hunters would start to show up to descend into the aforementioned caverns. It creates that adventurer's guild kind of vibe rather well.

That number is good, if you aim for somethin' very thematic and by the same time small at it's scale. You can't build a mountainhome, but you surely can create a small community, that you would remember even after a decade. I'd recommend to gradually increase your population cap as time passes. It works wonders both in terms of gameplay and narrative. It's only fair that migrants would show up in a place that has stood the test of time and is showin' a positive dynamic, right? I personally enjoy that feelin', when your cozy and tight-knit community becomes a busy and sprawlin' fortress over a century. When overly-decorated homes of your original 7 and a small tavern that had seen so many happy gatherings over a few decades makes way for a 3x3 modular bedrooms and a big, even over-sized tavern, as fortress goes deeper into the soil. When personality and community makes way for efficiency and productivity. When only memories remains. While it might be somber, it is also very real and believable experience, therefore losin' connection with characters becomes it's own plotline, a very personal one at that. Could argue that those emotional landscapes is the real !FUN! of the game, but I digress.

Hope that things above answered your question, albeit a little bit late.

Originally posted by XinZao:

I feel that more than that I'll lose conection with the characters, Can I be good only with 6 dwarfs?

Originally posted by 16 hour shift:

Almost two weeks has passed, no answer in sight, so I might as well give one.
In short -- yes, you can do that.
A more lengthy one goes below.

XinZao posted this in the workshop section, which might be why there hasn't been many responses lol.

Anyway, fully agree with 16 hour shift.

To add my own 2 cents, when I'm experimenting with new early game fort designs, I often will overly micromanage a new fort and expand rather slowly, and I often use the tutorial start to automatically pick a start location for me (with 7 dwarves) and then just skip the tutorial. Presumably due to something I'm doing, maybe not accruing enough wealth or something, I often end up with no extra migrants for a while, beyond the first wave that I think might come no matter what. This results in me having like 10'ish dwarves (more or less) for quite some time, that manage to sustain the fort just fine, albeit just much slower. You just have to assign more work details per dwarf, and make sure more time consuming work details don't eat up all of the work done, preventing important jobs from getting done (like stalling food production or something).

To add a couple more cents and maybe a different point of view... even when I get 100+ dwarves running around in a fort, I still tend to favor like 5 or 10 of them, that do very specific important jobs, or have done something at some point to make them stand out. Often it'll be some of my 7 original randomized starters. Like if I get a really good blacksmith, he/she ends up standing out to me, and I keep an eye out for events that might affect them beneficially or negatively. Maybe set them up a fancy work area. Then I also find myself reading their character page and taking note (or laughing) at their likes/dislikes, and generally.. still having a connection with that character, despite the 90 other background characters running amok.