Well, generally cats are about 1 lb per month... which would mean the *average* 7 month old cat would weigh about 7lbs. Now, your boy may be a larger build than average, but he may also weigh more than is ideal. I'll give you a link on how to evaluate the size of your cat and his "body condition score" which is a way of assessing whether they are over or under weight.
Obviously, I cannot make any comment on his weight without examining him... but I have rarely met a 7 month old kitten as large as 10-11lbs! ;-)
I advise most cat owners to switch to adult cat food at about 6 or 7 months of age, and I feel confident that your cat is ready to make the switch. The manufacturers of pet food would have you stay on kitten food much longer because it costs more. But he has reached 90% of his full height by now, so he would be fine to make the switch.
When switching to adult food, I recommend doing it over 2-3 weeks, with a gradual addition of the new food. So, start with 90% his regular and 10% the new food for 2 days, then 80% regular and 20% new, and so on. This will help prevent diarrhea or tummy upset.
Generally, the amount suggested on the bag of food is more than what a cat needs. Again, the manufacturers want to sell cat food, and they never want to be accused of starving a cat!
However, I don't feel comfortable with suggesting you cut back on the quantity without having actually seen the cat. The reason for my caution is that weight loss in cats can be tricky. If they lose weight too fast they are at serious risk of developing Hepatic Lipidosis (Fatty Liver Disease). This is something that overweight cats are prone to. If an overweight cat decreases his food consumption by approximately 30% for as little as 2 weeks he is likely to develop hepatic lipidosis. Also, if a fat cat stops eating completely for 2-3 days he is likely to develop hepatic lipidosis.
Essentially what happens is the body goes into a state of starvation, and a signal is sent out that the body must mobilize the fat stores to provide energy. Unfortunately, there doesn't seem to be a signal about how much fat to mobilize and fat cats have a lot... so it all gets sent to the liver to be converted from fat into glucose. And the liver gets overwhelmed and shuts down. This leads to nausea and vomiting, which means the cat won't eat, and the body tries to mobilize more fat. The cycle continues and the liver gets into more trouble.
I will add some links with further details:
So, in summary, most cats of this age weigh 7-8 lbs. And most cats of this age are ready to switch to adult food, so that is certainly a first step that you are safe to take with your boy. In terms of cutting back on the quantity, that is something that you would need to speak with your vet about directly as he would be in a better position to assess what would be safe for your kitty.
If this has been helpful, please accept my answer and leave feedback. I will still be here to provide more information if you need it!