Trunks was 8, Goten 7 when they were introduced. Only 10 years pass from Buu to Uub, this is in that gap. So its probable they are 11 and 10. Most interested in how an older Gotenks acts, but hey Billis is seen spanking him so he must still be a smart ass.
But yeah Tien supposedly got the third eye from enlightenment. It's an anomaly much like Krillin having no nose after his time being raised by the monks. And Yamcha is the one he gets it, he's the billionaire star baseball player, banging chicks left and right, while staying stronger than most in the universe but weaker than any of the Z fighters main group. 18 I guess is a technicality humas since she can reproduce as she's a cyborg, the present ones were written as Cyborgs in the manga (referred to as androids mistakenly in the dub), thus the free will and not killing everyone in sight like the walked out future versions in History of Trunks.
But yeah you're on point about Gohan, he was 17 (18 if you count the chamber) and Vegeta was expediting weaker but not weak and rusty too vs Dabura . He may be rusty here, but because it was a power given to him like with Guru, he should stay strong. That said it seems Vegeta and Goku got back to training as the SD manga released a preview of things and its Vegeta who is fighting Wiss who is also stronger than Goku/Gohan/Gotenks
I personally want to see the Z fighters and Vegeta fight together to take down Wiss whose the second strongest being in the universe, with Vegeta stepping up when all looks lost and ascending in battle like Goku and Gohan did at Feiza and Cell, while Goku takes on Billis as a ssgod in space.
[video=youtube;1z6rGVSwknA]http://www.youtube.com/watch?v=1z6rGVSwknA[/video]
Bonus character art