I think fabric manufacturers make it seem harder to make quilts for men and boys than it really is, because they have an interest in changing fashions for fabrics, and that means heavily promoting fabric sets, novelty fabrics and such.
As quite a few people have said here, most folk don't actually like novelty fabrics. They're not that high a proportion of fabrics anyway, but if they're what you're paying attention to, they'll seem like more. Men do not need trucks on their quilts to prove that they're men, and are likely to feel like they've been treated as children. Children don't need them either, and teenagers in particular are likely to feel condescended to, or just misread. I've never used one of those fabrics in my life, and I've made lots of quilts for babies, children, and adults of all genders. I've backed a couple of baby quilts with animal prints, owls were very in one year, and that's it. I prefer to make the shapes with the piecing, so one baby quilt had fish, another had a big turtle, and the dinosaur quilt was really popular. It surprised me how many adults said they'd have had that dinosaur quilt like a shot, although one woman was shocked that it was going to a wee girl.
Menswear in the west is terribly dull and lacking in colour. While a man may not want to buck the trend and wear brighter colours, although many do, it's not the same when it comes to quilts. A quilt is something kept in your home, mostly, it's not subject to the same social pressures as clothes. There is no reason to deprive men of colour! Of course they like colour! Even men I know who wear extraordinary amounts of grey want colour in their quilts! (Blues and greens for that friend, and he hung the quilt on the wall.)
It's odd that people feel under pressure to limit colours for men, like those discussions about football teams or what have you. About thirteen years ago, I bought a beautiful teal green bathrobe for my then-partner, which was the only nice colour in a depressing selection of grey, black, and colours striped with dull grey. He was thrilled. His grandfather made a crack about how it was the wrong colour, and we both had to spend quite a while figuring out that he was referring to the traditional football teams for that part of Scotland. My ex did not have the slightest interest in football, and I doubt anyone of his generation or younger would have cared about having a green bathrobe. When I say "his generation", he's forty now.
I'd avoid making something that looks like it's aimed at babies or old ladies, and also avoid anything that could be described as "screamingly girly" or "princessy". *But I would avoid that for absolutely everyone.*
Do you know who has really strong views about avoiding pink? It's women. Women who grew up being told they had to wear pink because they were girls, who found that everything marketed to them was pink and also twice the price. My mother was obsessed with pink and wore little else, which seriously put me off it. I'd have been deeply embarrassed and upset if someone had given me a pink and purple quilt at any point in my childhood, especially my teen years. I've got friends whose kids have a pink craze, so I'd do a pink quilt if requested, but you know, it's not always the girls having the pink craze. You can have a long and happy career as a quilter avoiding default pink.
The only time I've had pink requested in a quilt, it was because that friend (who is not a woman!) wanted the bi pride colours, which are pink, purple and blue. I went for hot pink, added in black and some orange to the purple and blue, and found that I really liked it. The quilt does not read as girly, it reads as vibrant.
If there's a bit of pink in there but the quilt is generally multicoloured, most people won't notice. Same goes for pastels. Look at all the mixes of colours in Kaffe Fassett prints, for instance. As for florals, a lot of them are really old-fashioned, like trying to reproduce quilts from the century before last. Assume that the vast majority of people want something modern, not something that their grandmother might have considered old-fashioned. Whereas if you have some fabrics which are leafy, and some which are sort of a large scale chrysanthemum in surprising colours, nah, it's not really a big deal.
Just put together nice combinations of colours and have fun. If you're struggling with colour, try a group of colours which are close together, and then an accent colour that's different. I have a lap quilt which is all earthy tones, rust and olive green and ochre and black and brown, and then little bits of a jade which reads as turquoise there. Or that blue and green quilt I made for a friend, that's largely blues and greens, some purples, and little pops of orange.
If it's going to teenagers, and especially teenagers who've had a hard time, please make some rainbow quilts. LGBTI teenagers are disproportionately likely to experience abuse, homelessness, the care system and such. Getting a rainbow quilt means the world to many of them. Rainbow quilts are also pretty universally popular, so many people find them cheering.