If your uncle tells you that your outfit is reminiscent of the way your mother dressed when she was young, it means your clothes remind him of your mother. Hopefully that doesn't mean your mother is still dressing you.
Reminiscent traces back to the Latin for "remember." If a house is reminiscent of your childhood home, it makes you remember your childhood home. Reminiscent can have a good or bad implication. If you tell someone that her paintings are reminiscent of a chimp's finger paintings, obviously that's not so good. But if you tell her that they're reminiscent of Dali, well that might be better.