I don't see a viable RS remake anytime soon due to the recent disaster in Japan due to the similarity Groudon and Kyogre share with nature. Second of all, 10 years after the 4th generation? Well, at least that means everyone is still young and kicking; nonetheless, Oak and Rowan would already be in their 60's and 70's. ;__;
However even if the fifth gen does have an RS remake, I expect the time machine to return since in the fifth generation "obtained from specific location" states that all generation III Pokemon ( from the GBA games ) say " traveled in a long period of time. " or something like that. Come to think of it, Mossdeep City would be the perfect place to have a time machine and it would work like how generation II did, only with differences. Now, since BW takes place ten years, a list of ages;
RGB-Red 10, Green 10, Blue 11, Yellow 10
Yellow-Red 12, Green 12, Blue 13, Yellow 11
GSC-Red 13, Green 13, Blue 14, Yellow 12, Gold 11, Silver 11, Kris 11
RS-Takes place 2-3 months after GSC; Ruby 10, Sapphire 10, Emerald 10
FRLG-Takes place sometime after the Sootopolis Crisis.
Emerald-2 or 3 weeks after FRLG as our heroes were turned to stone.
DP-Some weeks after Emerald and Riley made his cameo at the end of Emerald so it shouldn't be too long.
HGSS-the original RGBY gang don't appear for some reason. Gold, Silver, Kris are 16 I believe.
Platinum- Continuation to the end of DP.
BW- Ten years after DPPt-HGSS.
Your right, they could be in their early twenties
I revise oops......
RGB-Red, Green, Blue 11.
Yellow-Red, Green, Blue 13, Yellow 11.
GSC-Gold, Silver, Crys 11, Red, Green, Blue 14, Yellow 12.
RS-Ruby 11 (when start, he just reached 11) , Sapphire 10 (when conclusion, she 11)
FRLF-Red, Green, Blue 16, Yellow 14 , Silver 13, it's later to RS 6 7 months.
Emerald-Red, Green 16, Blue 17, Yellow 14, Gold (and he reach 14 age several days later), Silver, Crys 13 (it's not have mentioned Crys's age is 13 or 14 accurately, but treats as for the time being 13......), Ruby 12 (when start, he just reached 12) , Sapphire, Emerald 11, it's later to FRLF 2 3 months.
DP-Dia, Pearl, Platinum 12.
Pt-Platinum 12, it's later to DP 2 weeks appears.
HGSS-Gold, Silver, Crys 16, therefore we knew it's later to Emerald three years, and if Dia, Pearl, Platinum appears in HGSS, they will not surpass 14.
BW-It's unknown, but I guessed that they are 14 15. ;225;