I think it will be fine. In the last few seasons, the US version of DWTS have been trying to bring a younger demographic to the show by casting just 18 or even not quite 18 celebrities. The producers and pros have done a good job keeping the numbers age appropriate and not overtly sexy. And the male pros have been done a good job not dancing in an overtly sexy or romantic way with their younger partners.
You can just check out on YT the dances with Derek Hough and his 18/19 yr old partner Bethany Mota, Mark Ballas and 17 yr old Sadie Robertson from this past season. Their dances were all tastefully choreographed and performed. Unless the DWTS Russian producers are pushing a different angle, Gleb was on the US DWTS around this time and I'm sure will be taking notes from his US counterparts and how they handled having younger partners. Not to mention he was part of a trio number in season 16 of DWTS where he danced with an at the time 16 yr old Disney star competitor so he'll be used to it.
You can just check out on YT the dances with Derek Hough and his 18/19 yr old partner Bethany Mota, Mark Ballas and 17 yr old Sadie Robertson from this past season. Their dances were all tastefully choreographed and performed. Unless the DWTS Russian producers are pushing a different angle, Gleb was on the US DWTS around this time and I'm sure will be taking notes from his US counterparts and how they handled having younger partners. Not to mention he was part of a trio number in season 16 of DWTS where he danced with an at the time 16 yr old Disney star competitor so he'll be used to it.