Making your characters misanthropic is the quickest way to making them seem cool and misunderstood! ;>
Designing an older adult character? Draw them like your young characters, just add a single line under each eye. Lines around the mouth too if they're, like, super old.
More like a story tip BUT
Please make sure to have all romantic plots/subplots be incredibly obvious to your readers as soon as possible, preferable the nanosecond two characters meet. But ensure that the characters involved emphatically express how not-in-love they are with each other despite all evidence to the contrary. Bonus points for lines like "S-She's NOT my girlfriend!"