Completely disagree with people who say the extension is too long.
It's a pretty safe to bet on Suarez scoring 20+ goals per season even into his 30s. A player of his quality is more than capable of it.
Look at Eto'o, Drogba, Sneijder, Rooney, Van Persie etc. Players decline. Him being at a very high level at 34 is unlikely and a huge risk.