I do think the t-shirt/jeans combo works out for a Superman just starting off. Just about the execution
It totally makes sense... he's not going to want to wear a costume, in his younger years, it's about doing the rescue, defending someone, getting out... without getting caught on social media or the news. Think about it, what does he know of his alien heritage, does he trust this government.. he wears a t shirt under his clothes, rip them off - he's good to go...
Now, a cape? I don't think he has a cape straight away but there could be a very poignant scene where he saves a child and the child is like - you need a cape, you're a super hero! kind of thing..
My personal idea, for a reboot, is that he as a teenager is like the most advanced athlete ever, he enjoys sports and excels, but he doesn't push himself, he's never needed too, so he doesn't actually know how strong he is, he's modest too...
His eyes are also so sensitive, it's like he has over perfect eyes, so he wears glasses to kind of reign it In, as a teenager, he needs to control things - not in a bad way, but like a normal hormonal teenager.
The first movie, he's late 20's and he does feats around smallville, he confides in Lara - then, one evening, there isn charity wrestling match - he's involved and he wears the Kirk Allen super suit - he has a mask too. Other people are in other suits, Mexican style, it's fun, a typical fundraiser event.
Before Clark is about to enter the ring, as he's about to put on his mask, he hears and feels the vibrations of a train going too fast, in a neighbouring town... he can't explain it he just knows, so he's compelled to go go there.. he looks at Lana, explains, then opens a window and jumps out, takes massive strides and leaps, 100's of feet at a time, bursting over the horizon... he see's the train and catches up with it, it's an old tour train, he can see it's out of control, he is on top of a carriage, he retro suit looks amazing in action, the steam bellowing out and almost encases clark in an atmospheric fog, at this point fire trucks are ahead clearing the town, putting sound bags and barriers to protect, fearing the worst, hoping for the best... as the train turns a corner, those in the back can see the front carriages and clark on top...he jumps onto he connectors, separates the carriages, they instantly slow down... just left is the engine - clark jumps off and races against the vintage engine - it looks epic, dust and debris fly, then, clark gets infront, the tracks buckle, wood splintering off... the crew can see this red and blue object slowing down the train... he eventually stops it - media and bystanders take pictures, as a helicopter circles, - the broad shoulders and red cape, yellow s is visible as he turns around, to reveal an out of breath clark... his hands tremble with adrenaline, his chest heaving... clark suddenly focuses and realizes he needs to leave - he composes, is polite... semi salutes the fire chief from afar and bursts into the twilight sunset and dips away.
The media use that image, that's superman.. metropolis as an example starts selling blue t shirts with a cape for kids and tourists - all neighbouring cities do... why not? it's a gimmick and easy money - like big foot.
Clark then lays low.. worried a knock on his door will come, it never did... he resumes his heroic feats, a kid asks him, where is his cape? so it makes him think... also, Lana comes back from the city and is like, never guess what they are selling...shows him a caped t shirt... he thinks its just perfect and uses it... we follow him as he gets job offer at the daily planet, he currently works at the daily star.. and yeah the rest is history.
