It may be that on campaign it was difficult to keep the standards shown here, but as an officer, a clearly marked fashionable beard or moustache would have served to mark them out from rank and file
First up is the Earl of Sandwich painted by Walker. He's 25 and has the merest smudge on his top lip.
These guys, Richard Lovelace on the left and Thomas Killigrew below right were both about 28 when captured for posterity. Yet again, whether or not they could grow any more whiskers, both have seemed to opt for a top lip subtle moustache look.
Both Thomas and Richard were royalists but seem to have taken very small parts in the course of the war.
Richard Neville by Dobson at 30. First appearance of remaining whiskers below the bottom lip in this list.
William Dobson on the left was 35 when he painted himself. Small underlip thing going on here. William Ireton (39) on the right however has a full set coming up, though moustache and square goatee, like his friend Fairfax are still quite defined in this portrait by Walker. Maybe this was Henry after a week on campaign?
Oliver Cromwell seems to have a small moustache and tiny lower lip beard. He was 45 I think when Walker painted him here .
John Lord Byron below was also 45 when painted by Dobson. Nicely sculpted whiskers above and below the mouth.
Conyers Darcy at 52. Beginning to opt for something that covers at least part of the chin. Conyers was a nobleman who spent most of the war in the Houses of Parliament.
Nicholas Lanier, also painted with Dobson at 57 years of age. Big moustache and accompanying goatee beard. He was a musician at the court in Oxford.
Two guys aged 65. Inigo Jones has the full set of whiskers and Sir Thomas Aylesbury a decently (for his age) wide goatee covering his chin. Aylesbury was a Royalist and patron of mathematics. See comments below.