When I soon start Testosterone I hope it makes me more masculine..But I'm afraid I still won't pass since my hair is really long and I'm not even buff or tall. I don't know what I should do..Should I keep it?

I know a trans guy with long hair, whether it makes it harder for him to pass I don't know...he has a beard and is quite hairy, so the long hair probably doesn't matter much. Plus, now he's been on T for several years his hair when it's not tied back looks fairly oily and unkemp...nothing like female long hair.

Testosterone will bulk your upper half up to an extent which will help you out.
However, I've had a few guy friends over the years (bio males) that had long hair and I can tell you with honesty that even they were frequently misgendered from the back with the exception of the one that was 6'4" and bulkier than an ox up top. All of them found it pretty funny and enjoyed turning around to see the person recoil and start rapidly apologizing.
If your long hair makes you happy, keep it. Just be aware that the chances of you being misgendered are going to be much higher but not very different from what similar cisgender males face. I think if you go into knowing that you'll eventually be able to derive a little bit of humor from the situation just as they did.

Plenty of guys have long hair.  Most of them keep their hair long because they're too lazy to get it cut.  Guess how much time they put into styling it?  Forget everything you know about hair.

If your hair is straight, ponytail.  If your hair is curly, braid.  That's it for 99.9% of men's (very) long hair styles.  The ponytail should be sloppy, and the hair tie should be as low on the head as possible, right where your head turns into your neck.  Same goes for the braid, except you don't need a hair tie up top.  Since an additional hair tie requires more effort, you definitely don't want that.

Okay, now your hair is done.  Go to bed and don't mess with it in the morning. (this may be sarcasm, or it might work for you)

If you're a gross boy like I was, don't bother taking the braid down for the next month.  Then, the split ends will just break and break and break, and your braid will be a thin whippy rat tail at the end in no time at all.

All that said... my wife has done drag a couple of times, and tried to style her hair as above.  The result wasn't great.

If you want an intermediate-length hair cut, cut it straight at the shoulders; no layering, no funny stuff.

One thing to know about being a teenage boy with long hair: people are going to misgender you.  Maybe a lot.  It happens to cisgender male teenagers, as well.  A lot.

You don't have to let long hair be oily and gross for it to look masculine. I would actually suggest not letting it get that way.

A lot of guys have long hair and it seems to be a trend for guys to keep their hair longer these days so that'll definitely work to your advantage. Just try looking for some ideas on how to trim it or style it, you should be able to find tons of photos of guys with longer hair. There are a lot of YouTube videos too that have tutorials on how to masculinize long hair styles. I like this one:



The guy's hair in the video may be shorter than what you're thinking of but it shows how little details of a haircut can make the style more masculine.

Give T enough time and it'll masculinize your face to the point where you won't look anything but male. You probably will get misgendered from the back occasionally, even long haired cis guys do but if you're prepared to deal with that then go for it and keep your long hair!

I imagine even a small amount of stubble will be enough to indicate you're male, even with fairly long hair. Some degree of facial masculinization usually takes place, other cues like the voice, changing body shape/musculature etc. will contribute.

Man Bun. Give testosterone a few months your voice will be deep and you'll slowly start to have sideburns. That should be enough, especially if you're not currently overweight. For the time being I suggest you work out. Pushups and pull ups, build a bit of upper body.

T will def help you develop a masculine appearance.. But try getting an edge up at the barbershop. I once had long hair and it helped a lot. If not, you can always cut it. It's just hair.

Even though this Thread is a bit old, there are some things I'd take in consideration when talking or thinking about long hair and passing: The way you dress, the music you listen to and the people you spend your time with. Those often go hand in hand as there are certain subcultures/scenes where long hair isn't that unusual for men and being part of that sub-group can make things a lot easier.

I don't care if people misgender me from behind. Happens to cis guys I know with longer hair and if it doesn't bother them why should it bother me.

That said, if it contributes to not passing at all maybe get a shorter style while the T is doing its work. You can always grow it out later

(Not that I follow my own advice. I've become attached to my mane and don't want to give myself a stereotypical male cut just because "fitting in" or because it makes others more comfortable. Screw that)