photo credit: Plymouth City Council: Museum and Art Gallery
Should we believe the inscription, which says that this is someone aged 74 painted in 1596 (hence born c.1522), or that it is 'Sir John Hawkins', who was not born until 1532 and died in 1595? I guess the former.
As you say, the former. The Bodleian portrait shows him greying but still vigorous; the NMM one dated 1581 not grey at all. Both on Art UK.
This is a man older than he got to. Probably a case of Sir Wishful Thinking.
The inscription looks very plausible and correct to the period. Although the left part , the age seems it may have been tampered with. It would be good to take a closer look.The picture also looks like it has been enlarged. There is a definite line above the inscription and around the other tree sides suggesting the portrait was head and shoulders . It appears to have been more than doubled in size.. Possibly to conform with the conventional 50 x 40 size in British portraits.