The most important thing for Flynn in a partner right now is either someone who he doesn't feel will take sex too seriously or someone who he could have a genuine emotional connection with. LACKING THE LATTER, he's swinging a lot more toward the former. Flirting alone is sort of a new and exciting thing for him because he's never really had an interest in flirting or had a personal reason to do it. Flirting doesn't get you places in the Imperial Knights and before Aather that was his ~life~ so he just sort of ignored its existence.

But Aather is doing interesting things for Flynn in terms of developing his sense of self and sexuality is one of those facets. So he's more comfortable with flirting, mostly because if it works out nicely (like with Chariot) he feels flattered and he gets to flatter someone else so it's a win win situation. He definitely approaches people who are more laid back because this is new ground he's exploring. He already had a bit of a mess up with both Selenia and Yuri so he wants his exploration to be something he can do without worrying about long term repercussions for the relationship.

Also experience is nice because as earnest as he can be Flynn's (at this time) still a virgin. He wants someone who'd be more willing to show him the ropes and who knows their way around things so that he can get a better understanding of how things are done. He definitely won't go for a more inexperienced partner until he feels confident in his ability to please them.

I think the more that Flynn comes into a comfortable sense of his own sexuality the more comfortable he's going to be with things like physical affection and flirting. There's always going to be some degree of genuine affection behind it, though, because Flynn Scifo is not the kind of guy for one night stands. (unless it's something that the other party is completely comfortable with in which case, if they're attractive and he likes them, he's all for it)

Any memories in Yuri's registry that you're looking forward to?