Look at history. How many world class wingers are 33 or 34?
Nolito doesn't need to be worldclass, he just has to peform well when needed. And I think he can do that for at least 2-3 years. Remember that IF we buy him he'd be backup to our youngest starter (excluding Ter Stegen if he becomes our #1 GK) right now. In 2-3 years when Nolito will be "too old" Neymar will only come to his peak at 26-27 (IF we don't sell him but that's another story). For that I have absolutely no problem with Nolito's age if Lucho really wants him. We'd also have some flexibility with his signing and could play 4-2-3-1 with Nolito-Ney-Messi behind Suarez in some games with Busq-Raki as DMs.
Only problem is that Nolito can probably only replace Neymar without changing some of dynamics from our front 3 that worked so well over the last two seasons. Let's say that Suarez is unavailable for a longer period. Would we play Neymar as CF with Nolito and Messi on the wings? It certainly sounds better than relying on Munir like we did this season but can Ney really play that position effective against a great defense like Atletico? Maybe he can but we don't know and probably won't know until we try that. Messi as false 9 is another option but I just don't see him moving back to that position and I also don't think he can be as efficient in goalscoring role as he has been before Suarez's arrival.
That's why I said over the last months that I prefer a true CF like Gameiro to have a good backup for Suarez and we could go around this season with Arda, Rafinha and Denis playing on the wings when neccessary. But of course anyone has his price and I wouldn't pay more than 20M for Gameiro.
If there is really a possibility to get Vietto for around 20-25M I'd prefer him over both Gameiro and Nolito but I just don't see this happen. If Atletico decides to sell him it would be most likely to a club like Celta, Villarreal or Valencia for around 10M with buy back clause.