I hate the NTRP rating descriptions because they're so vague. The interesting thing, however, is that with very few exceptions, a 30 yr old 5.0 player will easily handle even the best of the junior players. Why? I don't know exactly, but having hit against my former coach who was a top 5 D1 college player and is now in his 30s and my current coach who was a former professional, it's not the same league as even hitting against an incoming D1 player. In a match, the young gun will likely have the stamina to win, but the years of wisdom just create an extra....edge.
Perfect example: a kid who I used to play with as a junior (he was very good for his age, so he played with us older kids) is now a 4 star (maybe 5, not sure as I don't really care because he's a pompous ***** with even worse parents). He's coached by the guy who runs where I used to play (aka, said former coach's boss). He was a former ATP player, top 300 maybe. Played in some majors nonetheless. Anyway, he's now in his 40s, doesn't play competitively in the slightest, and spends most of the day doing administrative work or teaching classes to 3.0 ladies. He and his student decided to play three practice matches. The first two were against my former coach, and the last against his own. The first match went something like 7-6, 6-4 to my old coach. This was actually surprising because he stays in shape and can still do serious damage even to the best juniors he coaches.
Next match, 6-1, 6-1. Turns out, the first match was a complete learning experience only. In other words, he was just given opportunities to work on shots, but purposely not allowed to win. The second go around was legitimate. When he played his current coach "all-out", it was bagels and breadsticks in an order I can't remember. Regardless, these guys are old, used to be great, and yet can still toy with nationally ranked juniors. It's amazing to watch that ability: go from making a 3.5 player look good by keeping rallies going during a lesson to making a great junior look amateurish by doing the same thing: just keeping rallies going. It's that ability, I think, that separates you from being a junior to being a senior player.