How do you approach physical boundaries on a first date when there’s a significant age gap (mid-20s vs early 50s), and one person has said they’re not into one-night stands or casual hookups?

Let’s say the vibe is good, there’s chemistry, and they haven’t explicitly ruled out something like a fwb situation. How do you balance showing interest without crossing a line or making things uncomfortable?

Has anyone been in this position or just have thoughts on how to approach the first date?