Devils mature at the same rate as a human but then at the age of 20... They appear to stop physically aging in terms of appearance, but they still age. A devil who's 20 is going to look 20 and be physically as healthy as someone who's 20 until they randomly die of old age at around 1,500 years of age, though while rare, some have lived to be 2,000 years of age under (again) rare circumstances.

 Additionally devils are medium sized beings, though they are on the upper end of the medium size class typically standing at around 6'8 to 6'10. Though you could rarely encounter one as short as a halfling, but that's rare.

Devils are usually evil aligned... However you can find ones that aren't if you're lucky.

Due to your devilish anatomy, you have resistance to fire damage and vulnerability to radiant damage.

 Due to your demonic lineage, you can move faster than what is normally possible and you can climb on any surface regardless of difficulty, including upside down on ceilings, without needing to make an ability check.

You have a movement speed and climbing speed of 35 ft.

 Due to your demonic origins, you are naturally stronger and more resistant then others. Which has led to excellent muscle definition and strength while not causing a very big increase in muscle size, devils of your type usually stand at around 6'8 to 6'10 on average due to bone density and size. While generally looking like a normal human, say for their size and naturally higher muscle definition which makes them occasionally be mistaken for just really short Goliaths whom have human skin tones.

 However you could potentially also have a few physical differences that affect your ability to function in day-to-day life, those traits have been outlined on the d12 table down below. You may pick 2 of these traits or roll 2d12 to decide which traits you get.