The English peerage was pretty small at the time. By my count:
47 Barons
2 Viscounts
22 Earls
1 Marquis
2 Dukes (the two Princes: Henry Frederick was Duke of Cornwall, and Charles was Duke of York)
Total: 74
I've had a look at all of these except the barons, and, assuming all died apart from Charles and Northumberland, it appears that 13 of the 27 titles would be held by people under 21, taking into account Writs of Acceleration and MPs. Of these, 3 were held by underage people anyway (including Prince Charles), who would presumably have been absent from Parliament. If they were present as spectators, then perhaps their titles would have been inherited by adults, thereby bringing them out of minority. Also, 5 titles above Baron would have become extinct, but only the Earls of Suffolk and Montgomery would otherwise had issue OTL. The Dukedom of York would (legally) be merged in the Crown, unless Elizabeth became Queen. Obviously, all of the new Lords would have been relatively politically inexperienced at first. Therefore, we could expect a greater reliance on both the the Commons and Scottish and Irish peers to run the country over the next few years.
The peerages above baronial rank in minority on 6 November 1605 would be:
- the Earldom of Cumberland
- the Earldom of Huntingdon
- the Earldom of Sussex
- the Earldom of Bath
- the Earldom of Bedford
- the Earldom of Pembroke
- the Earldom of Hertford
- the Earldom of Essex
- the Earldom of Devonshire
- the Earldom of Salisbury
- the Montagu Viscountcy
- the Lisle Viscountcy
plus Charles I.