So, I know that whenever you go to the doctor's or get weight loss advice, you are usually given a certain amount of calories that you should be eating based upon your gender. It's a well-known fact that male individuals tend to have a faster metabolism than female individuals, therefore they have to consume more daily calories. Also, identical body fat percentage looks drastically different on male and female bodies. Now, what I have been wondering is, should an FtM (or MtF for that matter) go by the male or female suggested calories when looking to lose or gain weight? If I have been on testosterone for five months, do I have the same metabolism as most normal cismales my age?

I would say this is an individual thing. The baseline calories for men and women are very loose guidelines.

My metabolism is still very slow, despite being on T for a while now. I can gain muscle easier but I still have to put in a lot of work and consume between 1100/1500 cals to lose fat. With 2000 being the recommendation for a female and 2500 for males you can see both of those would be way over what I need. Even to maintain my weight around 1800 is my maximum.

I know these figures because I have been tracking my calories/fat/carbs/protein and measuring results diligently since I started T and have perfected what works best for my body through trial and error and educated guesses.

Yeah I tend not to listen to the guidelines because everybody works differently. My partner pretty much lives off take away pizza and energy drinks and he really struggles to gain weight (I think he's about 9 stone/126 pounds/57kg) Whereas I have to be careful with what I consume. Energy drinks are the worst for me because of their sugar content, even though they tend not to have too many calories. I think I gained like 14 pounds in the space of a month from one energy drink a day.

Since starting T I've tried to watch what I eat as I was informed that T makes you gain weight but I'm hungry all the time and my body seems to be craving all kinds of stuff. I've been eating a lot of cakes and cookies (not the healthiest options, I know) but my weight has pretty much stayed the same so perhaps my metabolism is faster now. I'm not sure.

I just keep an eye on things. Some days I'll pig out but then i'll try and eat healthy the next day to balance it out a bit.

look at what you're already eating, and reduce it. 

Those guidelines are very general.  There are men who need to stick to salads and women who can eat for days without gaining weight.