Rainbows are the toughest for me to tell, because I don't catch them enough to get good at it maybe. Also, I think the wild fish we do have are closer genetically to the stocked strains. We don't have native rainbows, and the browns were established in like the late 1800's and early 1900's that were distributed as fry, before hatchery strains were really developed. Our few rainbow populations are descendents of more recent established hatchery strains. That's also why they are so rare, those strains just don't catch on easily (in the southern Appalachians they stocked rainbows earlier than PA did, and those strains were less hatcheryfied at that time).
Par marks are a poor indicator. A large fish with parr marks often means it's young but grew fast, size isn't always the best indicator of age, young fish in big water can be big because they grow fast. Small fish in small water can be old because they grow slow. Color is a poor indicator too, in all species, but especially bows because it's so diet influenced (just look how much steelhead change color after being in the stream a while). Piscavorous bows in big water are very silvery. Shrimp and scud eaters get a super bright stripe. And fish in streams get darker.
I have always noted that on wild fish, a white tip on the anal and pelvic fins is common. I won't use the term always (on wilds) or never (on stocked), but I've noticed that, and this thread bears it out some.
OP's fish is a hatchery fish, IMO.