It's iffy for me. It's difficult for me to think of just one of them and not make all their ages relative. So, there's a difference when I make an effort to do that v. the family as whole. But certain ones are still tied to each other, rather than independent (Bruce and Selina, Barbara and Jim, etc.)
When Bruce come to mind, it's the older Bruce with all of them there. Mid 40s.
Dick - always an adult by default in my head. Minimum 23, maximum 27, and working solo as Nightwing.
Alfred - he varies - I don't actually like him as Bruce's parent, but it's there. I tend to think of him as "15 years older than Bruce" but I'm really very variable and accepting of a wide variety of ages (not like he gets drawn a consistent relative age over the decades)
Barbara - also tend to think of in Oracle or post-Oracle phase - early 30s
Jason - I don't really follow the character, as I'm not an anti-hero guy. I tend to think of him as 20-23. This would not happen with me thinking of him relative to Dick and Tim (as a Batfam), because I hate him being made closer to Dick's age than Tim's - he's supposed to be no more than 2 years off Tim and at least 7 years off Dick.
Tim - Big division there. To me there are two Tims - the 15 year old solo-Robin series guy who lived with his dad and an 18/19 year-old independent Tim (neither Red Robin or Drake as a code name works for me, but he should get one of his own)
Steph - always the same age as Tim
Cass - still stuck in the past with her. Relative age would be 2 years older than Tim, but I still tend to think of her as 17/18
Damian - For a while I still thought of him as 10, since they spent a while recalcitrant to draw him older, and he was seemingly aged up for no other reason that to be a teen for Teen Titans, but the 13/14 year old is overtaking that now. Lack of kids Jon contributes.
Gordon - 25-35 years older than Barbara if I'm thinking about Barbara. If I'm not, then he's not a young man when he and Bruce meet and not yet retired when Damian arrives. Beyond that, I'm good.
Selina - within 2 years of Bruce's age (close enough to call "the same age" among people in their 20s). I hate her significantly younger and especially when she's made closer to Dick's age. I do have an attachment to their first meeting. When Dick is a kid and Robin and Bruce is in his mid-20s. She's an adult, a peer to Bruce when they meet. Not <21. And the timing of that meeting and them coming into each other's lives matters to me. I usually think of her in context of Bruce. Usually current day, so 40s, but if I'm thinking past, I line it up with how old Bruce should be.
Edit: I posted about this on
my Tumblr a few years ago. Opinions have moved a little since then as characters age, and those were all pegged relative (the entire family consistent instead picking each one at random points in time), and because I've grown increasingly unfond of Alfred raising Bruce the more I've thought about it.