General:
* Young
* New
* Fresh
* Recent
* Modern
* Current
* Up-to-date
More specific:
* Youthful: implies a youthful appearance or energy.
* Juvenile: implies immaturity.
* Immature: implies a lack of experience or development.
* Newborn: implies very young.
* Infant: implies very young.
* Childish: implies immaturity or lack of maturity.
* Teenage: implies a specific age range.
* Contemporary: implies something that is current or fashionable.
Opposite of aging:
* Ageless: implies a lack of visible signs of aging.
* Timeless: implies something that doesn't seem to age.
* Eternal: implies something that lasts forever.
In the context of objects:
* Used: implies something has been used but is not old.
* Second-hand: implies something is not new but not necessarily old.
* Vintage: implies something is old but still stylish or desirable.
The best word to use depends on the specific situation and what you want to emphasize.