Dude. Any excuse to have Colin Baker appear in modern Who is a good excuse. We now know as fact that Ten regenerated and kept his same form, because he was so attached to that body. Perhaps Maxil has regenerated half a dozen times since then, and kept the same form each time? If he had Colin Baker's striking good looks, why on Gallifrey would he want to change that?
I totally agree. Colin Baker is awesome, so really any excuse to see him would be awesome.
I like Colin Baker's expression in your av. It's like he's been listening to our conversation and thinking, "You know, I never thought about it like that. I got screwed!"

It's actually said in SJA that it's *rumoured* Ian and Babs don't age, not that they definitely don't.
How exactly would that work anyway? It doesn't seem to have affected Sarah Jane or Jo at all.
Might not be down to the Tardis, might be down to the Dalek time machine they used to get home?
OK, well that merely upgrades it from "nearly impossible" to "possible but makes no damn sense, totally random, and has no basis in anything previously established."