No, it does not affect ability scores - 5e removed the influence of a characters age to their ability points
There are no rules for adjusting ability scores based on the age of the adventurer. Your young Tiefling would have the same scores and proficiencies as he always had. In 5e age is just a fluff stat with no mechanical influence. While there are some effects like a ghosts Horrifying Visage that can magically age you just like Wild Magic can make you younger these don't have any influence on your character. See the question What are the effects of aging? that discusses this with a focus on a Monk's class feature Timeless Body which prevents the character from the frailty of old age. But there are no mechanics for the frailty of old age.
As always you can work out something with your GM - the starting point is the fluff text about the age of your race
The age can of course influence the roleplaying aspects of the game. For example there could be laws in your campaign about underage drinking in an Inn. Or you use the fluff texts of each race to find out when they become an adult and when they die. The texts are aimed at "normal" specimens of each race, but together with your DM you can work out how you want to handle this in your campaign.
There's precedent in the DMG to use the size of a creature for wearing armor and other items
If you insist on making a change to, for example, the equipment there are optional rules in the DMG that allow for armor of certain sizes. See page 140/141 "Wearing and Wielding Items" where it's explained that
if the story suggests a good reason for an item to fit only creatures of a certain size or shape, you can rule that it doesn't adjust. For example, drow-made armor might fit elves only.
Depending on how your group handles this you might want to make it your table's rule that armor has to be specifically crafted for someone to be used by him. Changing your age to something that would suddenly make an adult a kid could then mean that the armor doesn't fit anymore and has to be changed.
All other adaptations would have to be completely homebrewed.
(Disclaimer: I have never played 3.x and only read up a few minutes about how it was handled there and @KRyan, who mainly plays DnD 3.x, strongly advised against the following idea in a comment. This is just to give you an idea for what you could theoretically talk with your DM about.)
You could for example read up on how DnD 3.x handled this. According to @fectin, there were 4 different age categories and you would get +1 to your mental stats and -1 to your physical stats when changing to Middle aged. Old changes this to +2 for the mental stats and -3 to the physical stats. Venerable gives +3 to mental and -6 to physical stats. After that you get to the maximum age. There is no special category for children. You can try to create a table with age categories for every race in the campaign together with your GM to allow for a change of ability score by magically becoming younger/older.