I'm just commenting from what I've seen specifically with Cuadrado & Giovinco. I'm just saying that its worth being cautious with players who play wing positions or rely heavily on using their pace. Obviously, it isn't the case with all players.
There are obviously exceptions - Ronaldo trains harder than most players in the world, plus he is a top 2 player in the world. There are several examples of players being good into their 30s obviously, but it depends on the player.
If I'm buying a 27 year old player whose game is highly reliant on speed for $100MM, well I think that could be risky.
If you're buying a player with other characteristics, that doesn't apply - Totti for example was a beast at 30.
Exceptions: Pirlo, Totti, Del Piero, Ronaldo, Inzaghi, Iniesta, Xavi, De Rossi, Yaya Toure, Klose, Luca Toni....obviously there are tons of examples, and actually I believe players like Higuain will stay effective into their early 30s.
Examples: Sturridge, Kaka, Michael Owen, Lavezzi, Camoranesi, Zambrotta....those guys were arguably useless by 32.
Obviously, you just have to assess on a player by player basis - and if you're spending big, it's something worth considering for sure.