While 17 and 18 possess infinite energy and were somewhat evenly matched in the Cell Saga, 17 is much stronger than 18 now. Also, though Dragon Ball Super confirms that Android 18 is still stronger than Krillin, the difference between her and her husband may not be as large as it was once believed.
Are Android 17 and 18 stronger than Goku?
Android 18 is very likely on the same level as Piccolo or maybe slightly stronger or weaker. Android 17 on the other hand is definitely stronger than SSJG Goku but not stronger than SSJB Goku.
How old were Android 17 and 18?
Assuming their number designation could be a hint to their approximate age when they were introduced, as they were kidnapped as children, this would make both Android 17 and 18 in their late 20’s or early 30’s by the end of the Dragon Ball Super anime.