*sigh*
If folks would give more accurate "Subject" information, you'd be able to find the suggestions given to the last two or three people that have asked this. Then again, your answers will be visible to no one asking the same question, as your question isn't in the title of your post. It would be EXTREMELY cool of you to change the title to reflect the answers given, if folks are still of a mind to touch this topic, and I hope they are. I'd hate to think I was the only one to give opinion here.
Why? 'Cause my opinion is that you should mention it to her soon. Very soon. Don't wait, get deeply involved, and have to surpress an entire aspect of yourself to her. It's dishonest to you, and to her.
How soon? Depends on how she responds to BEING tickled. If she is playful, learn to tell her that you "really like her responses" and that you "always dig tickling". Play some more, assuming she's not giving you stinkeye, and then mention that it does something for you.
Then make sure you're ethical enough to avoid tickling other people, OR get into the discussion of tickling as a varied activity, tickling as being like kissing, etc. What do I mean? Like kissing, tickling can mean different things with different people involved. Picture kissing your mother, daughter, or aunt. If you kiss friends, point out how that's an entirely different act, but it still uses the same lips. Make it CLEAR where and when it's sexual, and, unless you're both polyamorous, don't tickle women that aren't familiar to you as friends or family. This, of course, assumes you can do so. I can. Some can't. No flaw if you can't, either. Just don't tickle anyone other than her. Treat it as it is for you, then. Like sex.
Now, if no one was going to respond before, at least you'll get more opinions now, as there are other points of view, and good ones, in my opinion. Just 'cause I ain't sayin' "keep quiet" or "don't ever tickle anyone else" doesn't mean that there aren't VALID opinions from others. What works for one may not for another.
Hope you get to where you feel good about this topic with your lover. Good luck!
dvnc