Wizards just buff or buff Wizards?

In my WIP, it is mostly study and practice that make a magic user. I think of it as somewhat akin to being musical and playing an instrument.
There are about half the people that just can't and [maybe because of that] have little or no use for magic.
There are some [most of the rest] that don't use magic, but if they had a teacher, a bit of time to practice and the willpower to put in the effort could produce something magical [a small charm or similar], someone strumming a guitar around a campfire.
A few have a bit of aptitude and [again] given a bit of instruction can get good enough to get paid for their magic. They usually have a few good spells but can do some other magic. Good enough to busk, form a band etc.
There are a few that are exceptional and can learn just about any magic they put their mind to given a chance. They may be exceptional in a few areas or not quite as good in a much wider area that is usual, your virtuous performers, session musicians.
And rarer still the creative, native magicians, the ones that don't need a teacher, they only have to see magic done before they can do it, or even just think it up themselves. Okay, quite a few of these tend to kill themselves accidentally while trying something out. These are the Beethovens and Bachs of my world.
There is little physicality to magic so any shape and size of person can be a magician. That said if a kid loves playing football or can earn more money on the Docks then they are not likely to want to be sent to a teacher to learn magic if they are not going to make a fortune from it. But as the mornings get earlier and the sack get harder, people might go back to magic as a second career. They can usually afford a better teacher and become a more able mage.

 

My wizards fall across the physical spectrum. Some examples:

Kyle of Bestia: You've seen his physical counterpart in multiple adventure flicks: pushing seven feet tall, massive beer belly, 300+ pounds, strong as the proverbial ox. A ugly vertical scar bisects the right side of his face (and almost cost him the eye). Looking at him, you'd think 'oafish peasant' (mostly true, he is of peasant stock), bandit (wrong, though he was in the legions), or thuggish innkeeper (maybe if events had gone differently). Very few would deduce he is a mage with talents in finding, fire, and fixing. Kyle can swing a sword, and isn't half bad at it..but he not the violent type at heart. The Traag War left him deeply scarred with what we'd call PTSD. Survived the Battle of Traag.

Doctor Isabella Menendez: An older woman, in the '100 pounds dripping wet' category. Isabella is not all that strong, but not frail, either: in 'Labyrinth: Journal' she kept walking pace with a band comprised of former imperial legionaries (though she didn't shoulder a full pack like they did). The sort who takes a three mile jog before a (healthy) breakfast. While she is a powerful sorceress, she's more of a scholarly sort. Definitely not the melee combat type.

Carina: Isabella's estranged granddaughter, orphaned by the war and drafted into the Arcane Cohort when the Empire learned of her occult abilities. She was all of ten. She proved lithe enough and savage enough to be placed on the teams sent out to assassinate Traag's demon conjuring sorcerers - teams that had extremely high fatality rates. At fifteen, she participated in and miraculously survived the Battle of Traag, where most of the cities million plus population perished in an insane demonic ritual. She was briefly possessed by a demon during that episode and had her powers blocked as a result. Carina is tough, but not really a straight up fighter.

Lysander of Equitant: A bit taller and a hair stronger than average. Served with the Empire in differing capacities all through the Traag War ('a twenty five year nightmare') ranging from training novice wizards (Kyle was among his pupils) to dangerous behind the lines missions to convoluted research. Accused of blasphemy an black magic at the wars end, went on the run for a while. Has an array of mostly minor psychological issues ranging from nightmares and talking to himself to a (fortunately mild) bipolar condition.

Pelopidas: Average height, large head atop a scrawny frame. Dextrose, but a bit on the weak side. Petty mage with a knack for illusions, a bit of a scholarly social climber. Not a melee fighter, offered bare bones magical instruction during the war.

Irwin: short and slight of frame, barely hitting the five foot mark, and just over 100 pounds in his heavy engineer boots. Traag war veteran, talented in rune magic, though his other arcane abilities are minor at best. Student (with Kyle) at the Enchanted Quadrant. Can fight, but is basically an engineer at heart.

Jack 'Handsome Jack,' : Irwin's companion. Definitely handsome, well proportioned, chiseled face, well mannered (being a house servant before the war). Modestly talented in finding, fire, and fixing, though he's acquired a few runes as well. Will fight if he has to, but prefers charm.

 

I d say it matters mostly in context to the character. My inspiration for magic users (and I know it is cheap, but bear with me) are my colleagues, since I work in the IT company. There are some general markings, but they come in all shapes and sizes—even the very good ones. We had an actual body-building medalist working as a developer, we also have this super-stereotype obese IT person with a very sad ponytail and bad posture. I think you can use the variety to your advantage.

If magic usage does request a certain physical strength, that s fine, but look at Olympic swimmers and weight-lifter. Both pretty muscular, but hardly the same. If there ware calories involved, I think, you d probably have a lot of obese mages (rather then strong ones), since I think it would be a general rule to overeat, just to keep with the demands of day-to-day spells. That s just human nature. If spell-casting required a perfectly choreographed tai-chi, you d have yourself super-fit bunch of mages. (They would have to spend hours making sure the chorography is perfect and hence would be forced to move and be in shape).

 

Depends on the magic and the user. I have one magic system based on smashing magic into metals. My MC is ripped AF.

Another magic system is based on legal principles. No need for a ripped bod.

My other system requires being in the good graces of some deity or bring s deity. My death god, being a forensic accountant, has a dad bod.