Can’t picture [name_m]Marvin[/name_m] on a little one really. I do like the nn [name_u]Vinny[/name_u] though!
I really like the suggestion of [name_u]Mars[/name_u]! Sounds fun and space like with him still having a solid name. I personally think of a leprechaun for some reason 
but that wouldn’t stop me from using it.
Marv and vin would be my go-to NNs.
Co,grats!
It makes me think of [name_m]Marvin[/name_m] [name_f]Gaye[/name_f].
Which makes me think of that one song let’s [name_m]Marvin[/name_m] [name_f]Gaye[/name_f] and get it on…
I love the name [name_m]Marvin[/name_m]. It has that vintage feel that you mentioned and it’s familiar.