Oh the old licensing laws! I remember I used to work in a petrol station in the north of England in 2009 and I used to get so much shit off customers when I had to refuse them because they looked under 25 even though they were clearly 18+. Problem is in the UK kids look a damn lot older than their actual age these days. so yeah good old British bureaucracy tries to sort out the problem by introducing bizarre laws like this one!
Anyway back to the main point, we're all going to age Valet. It's hard I know and I hate the thought too but its inevitable unfortunately. I am nearly 30 and am not looking forward to reaching that age. Having said that I've come across a lot of 30+ guys who look fucking sexy and I mean really hot and a lot younger than their actual age so you might still look younger for a few years yet.
Exercise and a good diet help a damn lot as well. But eventually you will age as we all do. But I would see it as an opportunity - with age comes wisdom and experience. That experience can be a good thing if done properly but if you worry about this too much it will damage your life experience and your mental well being if that makes sense?
Point is I would not let this get to you. Do you and this friend have something special going on may I ask? If so I wouldn't worry, if he really cares for you he won't leave or go anywhere even if there is a bit of an age gap.
To quote from a cheesy French pop song by TAL, eventually you will find 'Le Sens de la Vie'. I mean I know I can talk a bit, I have mild depression mostly caused by the stress of commuting and urban life in general but I know I have people who care for me and at the end of the day that is what's important - your spritual well being not your physical appearance (though physical health is still important).
Anyway I wouldn't worry, you probably look great the way you are
And as for plastic surgery - avoid it like the plague!! Seriously I wouldn't go for that unless you get involved in a serious accident and it becomes a medical requirement to get your face back to normal (or as close to 'normal' as possible).
Beauty products are okay in moderation but I would have ethical objections - some of them have been tested on animals so I would avoid those in my case. Plus they can be damned expensive!