I'm with Suresh.
No way a junior who might be a Number 1 singles in high school can go far in A/Open events. He might beat guys who don't belong there, like 4.5's who want to see how their game matches up, and they might beat another junior, but any experience adult would kill them 2's foreever.
Adult 5.0 is playing against experienced (more than 5 years of competitive tennis) full grown MEN, who can place serves, are not afraid of hitting head high topspin shots, and can volley and overhead better than anyone in juniors.
I played the #2 Junior in Peru, a then 16 year old, 5'11" and 170lbs. He was visiting CalBerkeley for a look at the campus. He crushed me, 2 and 2, but I was never better than 4.5, was over 55 at the time, and I could easily have taken more games if my ad court play was better. We played at least 6 doubles matches in the previous week, very evenly played.
I played the #4 singles player from DomincanCollege when I was maybe 45, almost 20 years after I made 4.5. He WON the junior Wimbledon the year before, and the match setup was via the coach, who wanted him to face a real lefty serve (he was lefty also). Very close match, him winning straight sets.
A full grown man who has tennis experience is not intimidated by little kids (under 17), no matter how hard they hit topspin groundies. Their serves and volleys are lacking, they don't position well at net, don't like to face skidding slices, and usually don't take practice matches seriously.
OTOH, now that I'm 63, I'm sure any top junior can hand me double bagels.