A few various unorganized thoughts:
[name_m]Dewey[/name_m] is amazing! I’ve rarely heard it mentioned here, but I love the versatile vintage sound. Connection to [name_m]David[/name_m] is cute! In all honesty, I’m not sure most kids these days even know what the [name_m]Dewey[/name_m] Decimal System is… so that wouldn’t really be an association to them anyways lol. Maybe paired with a more classic middle to balance it out: [name_m]Dewey[/name_m] [name_m]Benjamin[/name_m], [name_m]Dewey[/name_m] [name_m]Alexander[/name_m], [name_m]Dewey[/name_m] [name_m]James[/name_m], etc.
[name_m]Clifford[/name_m] “Kit” might work if you don’t like [name_m]Cliff[/name_m]! That’s always been my fave nickname for him.
[name_m]Albert[/name_m] is cool, and definitely a great alternative to [name_m]Gilbert[/name_m] if it doesn’t feel right to you. Maybe the nickname [name_m]Alby[/name_m] helps bridge that age gap between baby & older man? I met a middle aged man (maybe 40s?) called [name_m]Alby[/name_m] once! There’s also the [name_f]Maze[/name_f] Runner series which has an older-ish character named [name_m]Alby[/name_m] in it, who is my main association.
A few other random suggestions:
[name_m]Louie[/name_m], [name_m]Dawson[/name_m] / [name_m]Dawsey[/name_m] (means “son of David”), [name_f]Moe[/name_f], [name_m]Tolbert[/name_m] “Toby / [name_m]Bertie[/name_m] / Tolly”