If he can't accept the fact that you have epilepsy he can't accept you. Is he really worth the trouble.

Your age is a factor. There is no need to bring it up if after a few dates it fizzels out. In your 40's I would say you could mention it early on. It might help explain some of your possible deficits with memory and answer some of their secret questions they are afraid to ask.
In your twenties I would hold off until it's close to an I love you. Their brains aren't fully developed so they can't process the fact that epilepsy is about you and not how will it effect them right away. Twenty year olds need to have a solid connection so they don't just run and miss out on what you have to offer.
At 40 we want to know things up front but it's not needed if for at least a few dates. Just remember everyone thinks of epilepsy as rolling all over the floor looking like a dead fish. So immediately get that picture out of their head and explain the other kinds of seizures you have. Point out how independent you are and how it isn't always debilitating for you. Let them know it's not as if you are needing a care taker for a relationship. Your at a good age for this. Most men will just have questions and not "run".
I told my husband after a few weeks of seeing him on a 3-4 times a week basis. I was 28 at the time but he was 34. It didn't phase him. I wish you luck. It will work out for the best.

I always went on a few dates to see where it went. If we weren't going into a relationship I never told the person. If i knew we were getting close i told him right away so could decide if he could handle my epilepsy or not. I explained it to the fullest.

Has soon as possible so that they can make their own mind up quickly, and either leave or stay, saves you wondering what they are going to do

Second date. Use the first to leave an impression they will never forget and see you for YOU, NOT YOUR EPILEPSY!!! Plus, if you decide on a second date you both know you are both interested in each other and come the second date casually bring it up. I know....how do you casually bring up the fact you have an invisible illness and what it is? My answer? Be honest, be yourself, after all we want our partner to be themselves and be honest, so we need to do the same. Treat others the way you want to be treated.
I had experience with this not too long ago. I went out on a date with a guy I knew from high school, and I still liked him, so when I was asked on a second date I said yes. All the while saying to myself, "well you know he's interested, and he knows I'm interested, and since we are going on a second date he wants to learn more....Ok. Second date comes and I have no clue what I'm gonna do to "casually" bring up my invisible illness, and I felt very nervous and about halfway through our date it came out like word vomit. He and I were both shocked lol because I couldn't believe I just blurted that out, and he couldn't believe what he just heard. Initially he was scared to enter into a relationship with me and I flat out asked him if my epilepsy will be a deciding factor in our relationship, and at first he said yes. Girl, when he said yes, let me tell you, I layed into him lol. I asked him, "So your gonna let my epilepsy be the deciding factor on if you are gonna date me or not?" He said, "YES." I said, "wow, that's pretty Damn shallow of you. How you gonna let something I have no control over "decide" if you are gonna date me or not?!?! You have a heart condition right?!?! You have a timeframe on your life if you don't start taking care of yourself, and right now that's giving you 10 more years at the most, but am I letting your heart condition "decide" if I want to date you or not?!?! HELL NO!!! How would you feel if I did this to you and said I wasn't gonna date you because of your heart condition?!?! Not good I can tell ya that right now! It would make you feel as if your illness has taken over your life completely! I don't know about you but I'm much deeper than that, and if you decide to pass on it you will regret your decision because no matter what you decide I will leave this date with my head held high, my self-esteem and confidence level through the roof because I am in charge of my happiness and who I want in my life, not the other way around." And guess what? We are now engaged, just bought a house and after we get married he will be adopting my kids.