I-130 F4 Clarification on criteria of age

[Sinha]

I am an U.S. citizen, considering sponsoring my brother for U.S. green card. My brother has two sons, currently 15 and 18 years old. Me being from India, if approved it would take around 13 years for a visa number to be available for my brother's family.
Please help me to understand the following two questions I have:

1. Whether my brother's sons have to meet the criteria of age (below 21 years of age) a) at the time of application b) at the time of interview c) at time of entry to US. If it is NOT a) then I can safely rule out my nephews to get GC along with my brother.

2. My brother's son will be in a position to qualify for a H1 in another 3 to 4 years time. As he will be included in by brother's I-130, he probably has to mention in his H1 visa application that an immigrant visa application is pending for him. Will it adversely affect his chance of getting H1 for himself ?

Thanks in advance for any clarification and advice.

[curiousone]

...well at the time of application, they would have to be under 21 to b econsidered as children..........in certain circumstances, they can turn 21 and are still protected from "aging out" before they enter and I think before they interview if they turn 21 after the priority date becomes current but within a yr of the interview and Visa. However if the application takes 13 yrs as you say, its unlikely either son will be able to benefit as even the younger one will certainly turn 21 way before the priority date becomes current.

If I'm wrong, someone please correct me...